diff --git a/src/TUnit.Mocks.SourceGenerator/Builders/MockMembersBuilder.cs b/src/TUnit.Mocks.SourceGenerator/Builders/MockMembersBuilder.cs
index c92302750d..8453f5cf59 100644
--- a/src/TUnit.Mocks.SourceGenerator/Builders/MockMembersBuilder.cs
+++ b/src/TUnit.Mocks.SourceGenerator/Builders/MockMembersBuilder.cs
@@ -1251,7 +1251,7 @@ private static void EmitSingleFuncOverload(CodeWriter writer, MockMemberModel me
 
             if (funcIndices.Contains(i))
             {
-                paramParts.Add($"global::System.Func<{p.FullyQualifiedType}, bool> {p.Name}");
+                paramParts.Add($"global::System.Func<{p.FullyQualifiedType}, bool>? {p.Name}");
             }
             else if (p.IsRefStruct)
             {
@@ -1300,12 +1300,14 @@ private static void EmitSingleFuncOverload(CodeWriter writer, MockMemberModel me
 
             EmitOutParamDefaults(writer, method);
 
-            // Convert Func params to Arg<T> via implicit conversion
+            // A null predicate (including null/default literals) matches the parameter type’s default.
+            // This also handles value-type instantiations of unconstrained generic parameters.
+            // Keep non-null predicates on the existing implicit-conversion path.
             foreach (var idx in funcIndices.OrderBy(i => i))
             {
                 var p = method.Parameters[idx];
                 var rawName = p.Name.StartsWith("@", StringComparison.Ordinal) ? p.Name[1..] : p.Name;
-                writer.AppendLine($"global::TUnit.Mocks.Arguments.Arg<{p.FullyQualifiedType}> __fa_{rawName} = {p.Name};");
+                writer.AppendLine($"global::TUnit.Mocks.Arguments.Arg<{p.FullyQualifiedType}> __fa_{rawName} = {p.Name} is null ? global::TUnit.Mocks.Arguments.Arg.Is<{p.FullyQualifiedType}>(default({p.FullyQualifiedType})!) : (global::TUnit.Mocks.Arguments.Arg<{p.FullyQualifiedType}>){p.Name};");
             }
 
             // Build matchers array
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Closed_Generic_Usages_Snapshot.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Closed_Generic_Usages_Snapshot.verified.txt
index 13cb9b2a30..ee558f7d90 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Closed_Generic_Usages_Snapshot.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Closed_Generic_Usages_Snapshot.verified.txt
@@ -127,9 +127,9 @@ namespace TUnit.Mocks.Generated
             return new TestNamespace_IPair_TKey_TValue__Get_M0_MockCall<TKey, TValue>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Get", matchers);
         }
 
-        public static TestNamespace_IPair_TKey_TValue__Get_M0_MockCall<TKey, TValue> Get<TKey, TValue>(this global::TUnit.Mocks.Mock<global::TestNamespace.IPair<TKey, TValue>> mock, global::System.Func<TKey, bool> key)
+        public static TestNamespace_IPair_TKey_TValue__Get_M0_MockCall<TKey, TValue> Get<TKey, TValue>(this global::TUnit.Mocks.Mock<global::TestNamespace.IPair<TKey, TValue>> mock, global::System.Func<TKey, bool>? key)
         {
-            global::TUnit.Mocks.Arguments.Arg<TKey> __fa_key = key;
+            global::TUnit.Mocks.Arguments.Arg<TKey> __fa_key = key is null ? global::TUnit.Mocks.Arguments.Arg.Is<TKey>(default(TKey)!) : (global::TUnit.Mocks.Arguments.Arg<TKey>)key;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_key.Matcher };
             return new TestNamespace_IPair_TKey_TValue__Get_M0_MockCall<TKey, TValue>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Get", matchers);
         }
@@ -329,9 +329,9 @@ namespace TUnit.Mocks.Generated
             return new TestNamespace_IRepository_T__Find_M0_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Find", matchers);
         }
 
-        public static TestNamespace_IRepository_T__Find_M0_MockCall<T> Find<T>(this global::TUnit.Mocks.Mock<global::TestNamespace.IRepository<T>> mock, global::System.Func<int, bool> id)
+        public static TestNamespace_IRepository_T__Find_M0_MockCall<T> Find<T>(this global::TUnit.Mocks.Mock<global::TestNamespace.IRepository<T>> mock, global::System.Func<int, bool>? id)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_id = id;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_id = id is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)id;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_id.Matcher };
             return new TestNamespace_IRepository_T__Find_M0_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Find", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Colliding_Method_Type_Parameters_Snapshot.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Colliding_Method_Type_Parameters_Snapshot.verified.txt
index 857a844445..a3b2b757f2 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Colliding_Method_Type_Parameters_Snapshot.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Colliding_Method_Type_Parameters_Snapshot.verified.txt
@@ -74,10 +74,10 @@ namespace TestNamespace
             return new TestNamespace_IConstrained_T__Select_M0_MockCall<TMethod, TOther, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Select", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod, TOther>.Value);
         }
 
-        public TestNamespace_IConstrained_T__Select_M0_MockCall<TMethod, TOther, T> Select<TMethod, TOther>(global::System.Func<TMethod, bool> value) where TOther : TMethod
+        public TestNamespace_IConstrained_T__Select_M0_MockCall<TMethod, TOther, T> Select<TMethod, TOther>(global::System.Func<TMethod, bool>? value) where TOther : TMethod
         {
             var mock = this;
-            global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_value = value;
+            global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod>(default(TMethod)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod>)value;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_value.Matcher };
             return new TestNamespace_IConstrained_T__Select_M0_MockCall<TMethod, TOther, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Select", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod, TOther>.Value);
         }
@@ -159,9 +159,9 @@ namespace TUnit.Mocks.Generated
                 return new TestNamespace_IConstrained_T__Select_M0_MockCall<TMethod, TOther, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Select", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod, TOther>.Value);
             }
 
-            public TestNamespace_IConstrained_T__Select_M0_MockCall<TMethod, TOther, T> Select<TMethod, TOther>(global::System.Func<TMethod, bool> value) where TOther : TMethod
+            public TestNamespace_IConstrained_T__Select_M0_MockCall<TMethod, TOther, T> Select<TMethod, TOther>(global::System.Func<TMethod, bool>? value) where TOther : TMethod
             {
-                global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_value = value;
+                global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod>(default(TMethod)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod>)value;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_value.Matcher };
                 return new TestNamespace_IConstrained_T__Select_M0_MockCall<TMethod, TOther, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Select", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod, TOther>.Value);
             }
@@ -174,9 +174,9 @@ namespace TUnit.Mocks.Generated
                 return new TestNamespace_IConstrained_T__Select_M0_MockCall<TMethod, TOther, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Select", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod, TOther>.Value);
             }
 
-            public TestNamespace_IConstrained_T__Select_M0_MockCall<TMethod, TOther, T> Select<TMethod, TOther>(global::System.Func<TMethod, bool> value) where TOther : TMethod
+            public TestNamespace_IConstrained_T__Select_M0_MockCall<TMethod, TOther, T> Select<TMethod, TOther>(global::System.Func<TMethod, bool>? value) where TOther : TMethod
             {
-                global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_value = value;
+                global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod>(default(TMethod)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod>)value;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_value.Matcher };
                 return new TestNamespace_IConstrained_T__Select_M0_MockCall<TMethod, TOther, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Select", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod, TOther>.Value);
             }
@@ -312,10 +312,10 @@ namespace TestNamespace
             return new TestNamespace_IMethodNamed_T__TMethod_M0_MockCall<TMethod2, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "TMethod", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2>.Value);
         }
 
-        public TestNamespace_IMethodNamed_T__TMethod_M0_MockCall<TMethod2, T> TMethod<TMethod2>(global::System.Func<TMethod2, bool> value)
+        public TestNamespace_IMethodNamed_T__TMethod_M0_MockCall<TMethod2, T> TMethod<TMethod2>(global::System.Func<TMethod2, bool>? value)
         {
             var mock = this;
-            global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_value = value;
+            global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod2>(default(TMethod2)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod2>)value;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_value.Matcher };
             return new TestNamespace_IMethodNamed_T__TMethod_M0_MockCall<TMethod2, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "TMethod", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2>.Value);
         }
@@ -397,9 +397,9 @@ namespace TUnit.Mocks.Generated
                 return new TestNamespace_IMethodNamed_T__TMethod_M0_MockCall<TMethod2, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "TMethod", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2>.Value);
             }
 
-            public TestNamespace_IMethodNamed_T__TMethod_M0_MockCall<TMethod2, T> TMethod<TMethod2>(global::System.Func<TMethod2, bool> value)
+            public TestNamespace_IMethodNamed_T__TMethod_M0_MockCall<TMethod2, T> TMethod<TMethod2>(global::System.Func<TMethod2, bool>? value)
             {
-                global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_value = value;
+                global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod2>(default(TMethod2)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod2>)value;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_value.Matcher };
                 return new TestNamespace_IMethodNamed_T__TMethod_M0_MockCall<TMethod2, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "TMethod", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2>.Value);
             }
@@ -412,9 +412,9 @@ namespace TUnit.Mocks.Generated
                 return new TestNamespace_IMethodNamed_T__TMethod_M0_MockCall<TMethod2, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "TMethod", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2>.Value);
             }
 
-            public TestNamespace_IMethodNamed_T__TMethod_M0_MockCall<TMethod2, T> TMethod<TMethod2>(global::System.Func<TMethod2, bool> value)
+            public TestNamespace_IMethodNamed_T__TMethod_M0_MockCall<TMethod2, T> TMethod<TMethod2>(global::System.Func<TMethod2, bool>? value)
             {
-                global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_value = value;
+                global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod2>(default(TMethod2)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod2>)value;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_value.Matcher };
                 return new TestNamespace_IMethodNamed_T__TMethod_M0_MockCall<TMethod2, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "TMethod", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2>.Value);
             }
@@ -540,10 +540,10 @@ namespace TestNamespace
             return new TestNamespace_IOutbox_T__Invoke_M1_MockCall<TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Invoke", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod>.Value);
         }
 
-        public TestNamespace_IOutbox_T__Invoke_M1_MockCall<TMethod, T> Invoke<TMethod>(global::System.Func<object, bool> message)
+        public TestNamespace_IOutbox_T__Invoke_M1_MockCall<TMethod, T> Invoke<TMethod>(global::System.Func<object, bool>? message)
         {
             var mock = this;
-            global::TUnit.Mocks.Arguments.Arg<object> __fa_message = message;
+            global::TUnit.Mocks.Arguments.Arg<object> __fa_message = message is null ? global::TUnit.Mocks.Arguments.Arg.Is<object>(default(object)!) : (global::TUnit.Mocks.Arguments.Arg<object>)message;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_message.Matcher };
             return new TestNamespace_IOutbox_T__Invoke_M1_MockCall<TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Invoke", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod>.Value);
         }
@@ -632,9 +632,9 @@ namespace TUnit.Mocks.Generated
                 return new TestNamespace_IOutbox_T__Invoke_M1_MockCall<TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Invoke", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod>.Value);
             }
 
-            public TestNamespace_IOutbox_T__Invoke_M1_MockCall<TMethod, T> Invoke<TMethod>(global::System.Func<object, bool> message)
+            public TestNamespace_IOutbox_T__Invoke_M1_MockCall<TMethod, T> Invoke<TMethod>(global::System.Func<object, bool>? message)
             {
-                global::TUnit.Mocks.Arguments.Arg<object> __fa_message = message;
+                global::TUnit.Mocks.Arguments.Arg<object> __fa_message = message is null ? global::TUnit.Mocks.Arguments.Arg.Is<object>(default(object)!) : (global::TUnit.Mocks.Arguments.Arg<object>)message;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_message.Matcher };
                 return new TestNamespace_IOutbox_T__Invoke_M1_MockCall<TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Invoke", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod>.Value);
             }
@@ -647,9 +647,9 @@ namespace TUnit.Mocks.Generated
                 return new TestNamespace_IOutbox_T__Invoke_M1_MockCall<TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Invoke", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod>.Value);
             }
 
-            public TestNamespace_IOutbox_T__Invoke_M1_MockCall<TMethod, T> Invoke<TMethod>(global::System.Func<object, bool> message)
+            public TestNamespace_IOutbox_T__Invoke_M1_MockCall<TMethod, T> Invoke<TMethod>(global::System.Func<object, bool>? message)
             {
-                global::TUnit.Mocks.Arguments.Arg<object> __fa_message = message;
+                global::TUnit.Mocks.Arguments.Arg<object> __fa_message = message is null ? global::TUnit.Mocks.Arguments.Arg.Is<object>(default(object)!) : (global::TUnit.Mocks.Arguments.Arg<object>)message;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_message.Matcher };
                 return new TestNamespace_IOutbox_T__Invoke_M1_MockCall<TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Invoke", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod>.Value);
             }
@@ -791,27 +791,27 @@ namespace TestNamespace
             return new TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Invoke", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2>.Value);
         }
 
-        public TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T> Invoke<TMethod2>(global::System.Func<int, bool> TMethod, global::TUnit.Mocks.Arguments.Arg<TMethod2> value)
+        public TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T> Invoke<TMethod2>(global::System.Func<int, bool>? TMethod, global::TUnit.Mocks.Arguments.Arg<TMethod2> value)
         {
             var mock = this;
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_TMethod = TMethod;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_TMethod = TMethod is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)TMethod;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_TMethod.Matcher, value.Matcher };
             return new TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Invoke", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2>.Value);
         }
 
-        public TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T> Invoke<TMethod2>(global::TUnit.Mocks.Arguments.Arg<int> TMethod, global::System.Func<TMethod2, bool> value)
+        public TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T> Invoke<TMethod2>(global::TUnit.Mocks.Arguments.Arg<int> TMethod, global::System.Func<TMethod2, bool>? value)
         {
             var mock = this;
-            global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_value = value;
+            global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod2>(default(TMethod2)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod2>)value;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { TMethod.Matcher, __fa_value.Matcher };
             return new TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Invoke", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2>.Value);
         }
 
-        public TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T> Invoke<TMethod2>(global::System.Func<int, bool> TMethod, global::System.Func<TMethod2, bool> value)
+        public TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T> Invoke<TMethod2>(global::System.Func<int, bool>? TMethod, global::System.Func<TMethod2, bool>? value)
         {
             var mock = this;
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_TMethod = TMethod;
-            global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_value = value;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_TMethod = TMethod is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)TMethod;
+            global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod2>(default(TMethod2)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod2>)value;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_TMethod.Matcher, __fa_value.Matcher };
             return new TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Invoke", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2>.Value);
         }
@@ -893,24 +893,24 @@ namespace TUnit.Mocks.Generated
                 return new TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Invoke", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2>.Value);
             }
 
-            public TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T> Invoke<TMethod2>(global::System.Func<int, bool> TMethod, global::TUnit.Mocks.Arguments.Arg<TMethod2> value)
+            public TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T> Invoke<TMethod2>(global::System.Func<int, bool>? TMethod, global::TUnit.Mocks.Arguments.Arg<TMethod2> value)
             {
-                global::TUnit.Mocks.Arguments.Arg<int> __fa_TMethod = TMethod;
+                global::TUnit.Mocks.Arguments.Arg<int> __fa_TMethod = TMethod is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)TMethod;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_TMethod.Matcher, value.Matcher };
                 return new TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Invoke", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2>.Value);
             }
 
-            public TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T> Invoke<TMethod2>(global::TUnit.Mocks.Arguments.Arg<int> TMethod, global::System.Func<TMethod2, bool> value)
+            public TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T> Invoke<TMethod2>(global::TUnit.Mocks.Arguments.Arg<int> TMethod, global::System.Func<TMethod2, bool>? value)
             {
-                global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_value = value;
+                global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod2>(default(TMethod2)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod2>)value;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { TMethod.Matcher, __fa_value.Matcher };
                 return new TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Invoke", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2>.Value);
             }
 
-            public TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T> Invoke<TMethod2>(global::System.Func<int, bool> TMethod, global::System.Func<TMethod2, bool> value)
+            public TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T> Invoke<TMethod2>(global::System.Func<int, bool>? TMethod, global::System.Func<TMethod2, bool>? value)
             {
-                global::TUnit.Mocks.Arguments.Arg<int> __fa_TMethod = TMethod;
-                global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_value = value;
+                global::TUnit.Mocks.Arguments.Arg<int> __fa_TMethod = TMethod is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)TMethod;
+                global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod2>(default(TMethod2)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod2>)value;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_TMethod.Matcher, __fa_value.Matcher };
                 return new TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Invoke", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2>.Value);
             }
@@ -923,24 +923,24 @@ namespace TUnit.Mocks.Generated
                 return new TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Invoke", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2>.Value);
             }
 
-            public TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T> Invoke<TMethod2>(global::System.Func<int, bool> TMethod, global::TUnit.Mocks.Arguments.Arg<TMethod2> value)
+            public TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T> Invoke<TMethod2>(global::System.Func<int, bool>? TMethod, global::TUnit.Mocks.Arguments.Arg<TMethod2> value)
             {
-                global::TUnit.Mocks.Arguments.Arg<int> __fa_TMethod = TMethod;
+                global::TUnit.Mocks.Arguments.Arg<int> __fa_TMethod = TMethod is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)TMethod;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_TMethod.Matcher, value.Matcher };
                 return new TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Invoke", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2>.Value);
             }
 
-            public TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T> Invoke<TMethod2>(global::TUnit.Mocks.Arguments.Arg<int> TMethod, global::System.Func<TMethod2, bool> value)
+            public TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T> Invoke<TMethod2>(global::TUnit.Mocks.Arguments.Arg<int> TMethod, global::System.Func<TMethod2, bool>? value)
             {
-                global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_value = value;
+                global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod2>(default(TMethod2)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod2>)value;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { TMethod.Matcher, __fa_value.Matcher };
                 return new TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Invoke", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2>.Value);
             }
 
-            public TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T> Invoke<TMethod2>(global::System.Func<int, bool> TMethod, global::System.Func<TMethod2, bool> value)
+            public TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T> Invoke<TMethod2>(global::System.Func<int, bool>? TMethod, global::System.Func<TMethod2, bool>? value)
             {
-                global::TUnit.Mocks.Arguments.Arg<int> __fa_TMethod = TMethod;
-                global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_value = value;
+                global::TUnit.Mocks.Arguments.Arg<int> __fa_TMethod = TMethod is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)TMethod;
+                global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod2>(default(TMethod2)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod2>)value;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_TMethod.Matcher, __fa_value.Matcher };
                 return new TestNamespace_IParameterNamed_T__Invoke_M0_MockCall<TMethod2, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Invoke", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2>.Value);
             }
@@ -1069,27 +1069,27 @@ namespace TestNamespace
             return new TestNamespace_IStore_T__Put_M0_MockCall<TKey, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Put", matchers, global::TUnit.Mocks.TypeArguments.Of<TKey>.Value);
         }
 
-        public TestNamespace_IStore_T__Put_M0_MockCall<TKey, T> Put<TKey>(global::System.Func<TKey, bool> key, global::TUnit.Mocks.Arguments.Arg<T> value) where TKey : notnull
+        public TestNamespace_IStore_T__Put_M0_MockCall<TKey, T> Put<TKey>(global::System.Func<TKey, bool>? key, global::TUnit.Mocks.Arguments.Arg<T> value) where TKey : notnull
         {
             var mock = this;
-            global::TUnit.Mocks.Arguments.Arg<TKey> __fa_key = key;
+            global::TUnit.Mocks.Arguments.Arg<TKey> __fa_key = key is null ? global::TUnit.Mocks.Arguments.Arg.Is<TKey>(default(TKey)!) : (global::TUnit.Mocks.Arguments.Arg<TKey>)key;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_key.Matcher, value.Matcher };
             return new TestNamespace_IStore_T__Put_M0_MockCall<TKey, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Put", matchers, global::TUnit.Mocks.TypeArguments.Of<TKey>.Value);
         }
 
-        public TestNamespace_IStore_T__Put_M0_MockCall<TKey, T> Put<TKey>(global::TUnit.Mocks.Arguments.Arg<TKey> key, global::System.Func<T, bool> value) where TKey : notnull
+        public TestNamespace_IStore_T__Put_M0_MockCall<TKey, T> Put<TKey>(global::TUnit.Mocks.Arguments.Arg<TKey> key, global::System.Func<T, bool>? value) where TKey : notnull
         {
             var mock = this;
-            global::TUnit.Mocks.Arguments.Arg<T> __fa_value = value;
+            global::TUnit.Mocks.Arguments.Arg<T> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<T>(default(T)!) : (global::TUnit.Mocks.Arguments.Arg<T>)value;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { key.Matcher, __fa_value.Matcher };
             return new TestNamespace_IStore_T__Put_M0_MockCall<TKey, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Put", matchers, global::TUnit.Mocks.TypeArguments.Of<TKey>.Value);
         }
 
-        public TestNamespace_IStore_T__Put_M0_MockCall<TKey, T> Put<TKey>(global::System.Func<TKey, bool> key, global::System.Func<T, bool> value) where TKey : notnull
+        public TestNamespace_IStore_T__Put_M0_MockCall<TKey, T> Put<TKey>(global::System.Func<TKey, bool>? key, global::System.Func<T, bool>? value) where TKey : notnull
         {
             var mock = this;
-            global::TUnit.Mocks.Arguments.Arg<TKey> __fa_key = key;
-            global::TUnit.Mocks.Arguments.Arg<T> __fa_value = value;
+            global::TUnit.Mocks.Arguments.Arg<TKey> __fa_key = key is null ? global::TUnit.Mocks.Arguments.Arg.Is<TKey>(default(TKey)!) : (global::TUnit.Mocks.Arguments.Arg<TKey>)key;
+            global::TUnit.Mocks.Arguments.Arg<T> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<T>(default(T)!) : (global::TUnit.Mocks.Arguments.Arg<T>)value;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_key.Matcher, __fa_value.Matcher };
             return new TestNamespace_IStore_T__Put_M0_MockCall<TKey, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Put", matchers, global::TUnit.Mocks.TypeArguments.Of<TKey>.Value);
         }
@@ -1103,10 +1103,10 @@ namespace TestNamespace
             return new TestNamespace_IStore_T__Convert_M1_MockCall<TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Convert", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod>.Value);
         }
 
-        public TestNamespace_IStore_T__Convert_M1_MockCall<TMethod, T> Convert<TMethod>(global::System.Func<TMethod, bool> value)
+        public TestNamespace_IStore_T__Convert_M1_MockCall<TMethod, T> Convert<TMethod>(global::System.Func<TMethod, bool>? value)
         {
             var mock = this;
-            global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_value = value;
+            global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod>(default(TMethod)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod>)value;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_value.Matcher };
             return new TestNamespace_IStore_T__Convert_M1_MockCall<TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Convert", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod>.Value);
         }
@@ -1193,24 +1193,24 @@ namespace TUnit.Mocks.Generated
                 return new TestNamespace_IStore_T__Put_M0_MockCall<TKey, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Put", matchers, global::TUnit.Mocks.TypeArguments.Of<TKey>.Value);
             }
 
-            public TestNamespace_IStore_T__Put_M0_MockCall<TKey, T> Put<TKey>(global::System.Func<TKey, bool> key, global::TUnit.Mocks.Arguments.Arg<T> value) where TKey : notnull
+            public TestNamespace_IStore_T__Put_M0_MockCall<TKey, T> Put<TKey>(global::System.Func<TKey, bool>? key, global::TUnit.Mocks.Arguments.Arg<T> value) where TKey : notnull
             {
-                global::TUnit.Mocks.Arguments.Arg<TKey> __fa_key = key;
+                global::TUnit.Mocks.Arguments.Arg<TKey> __fa_key = key is null ? global::TUnit.Mocks.Arguments.Arg.Is<TKey>(default(TKey)!) : (global::TUnit.Mocks.Arguments.Arg<TKey>)key;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_key.Matcher, value.Matcher };
                 return new TestNamespace_IStore_T__Put_M0_MockCall<TKey, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Put", matchers, global::TUnit.Mocks.TypeArguments.Of<TKey>.Value);
             }
 
-            public TestNamespace_IStore_T__Put_M0_MockCall<TKey, T> Put<TKey>(global::TUnit.Mocks.Arguments.Arg<TKey> key, global::System.Func<T, bool> value) where TKey : notnull
+            public TestNamespace_IStore_T__Put_M0_MockCall<TKey, T> Put<TKey>(global::TUnit.Mocks.Arguments.Arg<TKey> key, global::System.Func<T, bool>? value) where TKey : notnull
             {
-                global::TUnit.Mocks.Arguments.Arg<T> __fa_value = value;
+                global::TUnit.Mocks.Arguments.Arg<T> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<T>(default(T)!) : (global::TUnit.Mocks.Arguments.Arg<T>)value;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { key.Matcher, __fa_value.Matcher };
                 return new TestNamespace_IStore_T__Put_M0_MockCall<TKey, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Put", matchers, global::TUnit.Mocks.TypeArguments.Of<TKey>.Value);
             }
 
-            public TestNamespace_IStore_T__Put_M0_MockCall<TKey, T> Put<TKey>(global::System.Func<TKey, bool> key, global::System.Func<T, bool> value) where TKey : notnull
+            public TestNamespace_IStore_T__Put_M0_MockCall<TKey, T> Put<TKey>(global::System.Func<TKey, bool>? key, global::System.Func<T, bool>? value) where TKey : notnull
             {
-                global::TUnit.Mocks.Arguments.Arg<TKey> __fa_key = key;
-                global::TUnit.Mocks.Arguments.Arg<T> __fa_value = value;
+                global::TUnit.Mocks.Arguments.Arg<TKey> __fa_key = key is null ? global::TUnit.Mocks.Arguments.Arg.Is<TKey>(default(TKey)!) : (global::TUnit.Mocks.Arguments.Arg<TKey>)key;
+                global::TUnit.Mocks.Arguments.Arg<T> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<T>(default(T)!) : (global::TUnit.Mocks.Arguments.Arg<T>)value;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_key.Matcher, __fa_value.Matcher };
                 return new TestNamespace_IStore_T__Put_M0_MockCall<TKey, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Put", matchers, global::TUnit.Mocks.TypeArguments.Of<TKey>.Value);
             }
@@ -1223,24 +1223,24 @@ namespace TUnit.Mocks.Generated
                 return new TestNamespace_IStore_T__Put_M0_MockCall<TKey, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Put", matchers, global::TUnit.Mocks.TypeArguments.Of<TKey>.Value);
             }
 
-            public TestNamespace_IStore_T__Put_M0_MockCall<TKey, T> Put<TKey>(global::System.Func<TKey, bool> key, global::TUnit.Mocks.Arguments.Arg<T> value) where TKey : notnull
+            public TestNamespace_IStore_T__Put_M0_MockCall<TKey, T> Put<TKey>(global::System.Func<TKey, bool>? key, global::TUnit.Mocks.Arguments.Arg<T> value) where TKey : notnull
             {
-                global::TUnit.Mocks.Arguments.Arg<TKey> __fa_key = key;
+                global::TUnit.Mocks.Arguments.Arg<TKey> __fa_key = key is null ? global::TUnit.Mocks.Arguments.Arg.Is<TKey>(default(TKey)!) : (global::TUnit.Mocks.Arguments.Arg<TKey>)key;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_key.Matcher, value.Matcher };
                 return new TestNamespace_IStore_T__Put_M0_MockCall<TKey, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Put", matchers, global::TUnit.Mocks.TypeArguments.Of<TKey>.Value);
             }
 
-            public TestNamespace_IStore_T__Put_M0_MockCall<TKey, T> Put<TKey>(global::TUnit.Mocks.Arguments.Arg<TKey> key, global::System.Func<T, bool> value) where TKey : notnull
+            public TestNamespace_IStore_T__Put_M0_MockCall<TKey, T> Put<TKey>(global::TUnit.Mocks.Arguments.Arg<TKey> key, global::System.Func<T, bool>? value) where TKey : notnull
             {
-                global::TUnit.Mocks.Arguments.Arg<T> __fa_value = value;
+                global::TUnit.Mocks.Arguments.Arg<T> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<T>(default(T)!) : (global::TUnit.Mocks.Arguments.Arg<T>)value;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { key.Matcher, __fa_value.Matcher };
                 return new TestNamespace_IStore_T__Put_M0_MockCall<TKey, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Put", matchers, global::TUnit.Mocks.TypeArguments.Of<TKey>.Value);
             }
 
-            public TestNamespace_IStore_T__Put_M0_MockCall<TKey, T> Put<TKey>(global::System.Func<TKey, bool> key, global::System.Func<T, bool> value) where TKey : notnull
+            public TestNamespace_IStore_T__Put_M0_MockCall<TKey, T> Put<TKey>(global::System.Func<TKey, bool>? key, global::System.Func<T, bool>? value) where TKey : notnull
             {
-                global::TUnit.Mocks.Arguments.Arg<TKey> __fa_key = key;
-                global::TUnit.Mocks.Arguments.Arg<T> __fa_value = value;
+                global::TUnit.Mocks.Arguments.Arg<TKey> __fa_key = key is null ? global::TUnit.Mocks.Arguments.Arg.Is<TKey>(default(TKey)!) : (global::TUnit.Mocks.Arguments.Arg<TKey>)key;
+                global::TUnit.Mocks.Arguments.Arg<T> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<T>(default(T)!) : (global::TUnit.Mocks.Arguments.Arg<T>)value;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_key.Matcher, __fa_value.Matcher };
                 return new TestNamespace_IStore_T__Put_M0_MockCall<TKey, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Put", matchers, global::TUnit.Mocks.TypeArguments.Of<TKey>.Value);
             }
@@ -1254,9 +1254,9 @@ namespace TUnit.Mocks.Generated
                 return new TestNamespace_IStore_T__Convert_M1_MockCall<TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Convert", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod>.Value);
             }
 
-            public TestNamespace_IStore_T__Convert_M1_MockCall<TMethod, T> Convert<TMethod>(global::System.Func<TMethod, bool> value)
+            public TestNamespace_IStore_T__Convert_M1_MockCall<TMethod, T> Convert<TMethod>(global::System.Func<TMethod, bool>? value)
             {
-                global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_value = value;
+                global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod>(default(TMethod)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod>)value;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_value.Matcher };
                 return new TestNamespace_IStore_T__Convert_M1_MockCall<TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Convert", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod>.Value);
             }
@@ -1269,9 +1269,9 @@ namespace TUnit.Mocks.Generated
                 return new TestNamespace_IStore_T__Convert_M1_MockCall<TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Convert", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod>.Value);
             }
 
-            public TestNamespace_IStore_T__Convert_M1_MockCall<TMethod, T> Convert<TMethod>(global::System.Func<TMethod, bool> value)
+            public TestNamespace_IStore_T__Convert_M1_MockCall<TMethod, T> Convert<TMethod>(global::System.Func<TMethod, bool>? value)
             {
-                global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_value = value;
+                global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod>(default(TMethod)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod>)value;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_value.Matcher };
                 return new TestNamespace_IStore_T__Convert_M1_MockCall<TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Convert", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod>.Value);
             }
@@ -1428,27 +1428,27 @@ namespace TestNamespace
             return new TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Use", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2, TMethod>.Value);
         }
 
-        public TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T> Use<TMethod2, TMethod>(global::System.Func<TMethod2, bool> first, global::TUnit.Mocks.Arguments.Arg<TMethod> second)
+        public TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T> Use<TMethod2, TMethod>(global::System.Func<TMethod2, bool>? first, global::TUnit.Mocks.Arguments.Arg<TMethod> second)
         {
             var mock = this;
-            global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_first = first;
+            global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_first = first is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod2>(default(TMethod2)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod2>)first;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_first.Matcher, second.Matcher };
             return new TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Use", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2, TMethod>.Value);
         }
 
-        public TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T> Use<TMethod2, TMethod>(global::TUnit.Mocks.Arguments.Arg<TMethod2> first, global::System.Func<TMethod, bool> second)
+        public TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T> Use<TMethod2, TMethod>(global::TUnit.Mocks.Arguments.Arg<TMethod2> first, global::System.Func<TMethod, bool>? second)
         {
             var mock = this;
-            global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_second = second;
+            global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_second = second is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod>(default(TMethod)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod>)second;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { first.Matcher, __fa_second.Matcher };
             return new TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Use", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2, TMethod>.Value);
         }
 
-        public TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T> Use<TMethod2, TMethod>(global::System.Func<TMethod2, bool> first, global::System.Func<TMethod, bool> second)
+        public TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T> Use<TMethod2, TMethod>(global::System.Func<TMethod2, bool>? first, global::System.Func<TMethod, bool>? second)
         {
             var mock = this;
-            global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_first = first;
-            global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_second = second;
+            global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_first = first is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod2>(default(TMethod2)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod2>)first;
+            global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_second = second is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod>(default(TMethod)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod>)second;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_first.Matcher, __fa_second.Matcher };
             return new TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Use", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2, TMethod>.Value);
         }
@@ -1530,24 +1530,24 @@ namespace TUnit.Mocks.Generated
                 return new TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Use", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2, TMethod>.Value);
             }
 
-            public TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T> Use<TMethod2, TMethod>(global::System.Func<TMethod2, bool> first, global::TUnit.Mocks.Arguments.Arg<TMethod> second)
+            public TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T> Use<TMethod2, TMethod>(global::System.Func<TMethod2, bool>? first, global::TUnit.Mocks.Arguments.Arg<TMethod> second)
             {
-                global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_first = first;
+                global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_first = first is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod2>(default(TMethod2)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod2>)first;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_first.Matcher, second.Matcher };
                 return new TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Use", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2, TMethod>.Value);
             }
 
-            public TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T> Use<TMethod2, TMethod>(global::TUnit.Mocks.Arguments.Arg<TMethod2> first, global::System.Func<TMethod, bool> second)
+            public TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T> Use<TMethod2, TMethod>(global::TUnit.Mocks.Arguments.Arg<TMethod2> first, global::System.Func<TMethod, bool>? second)
             {
-                global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_second = second;
+                global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_second = second is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod>(default(TMethod)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod>)second;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { first.Matcher, __fa_second.Matcher };
                 return new TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Use", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2, TMethod>.Value);
             }
 
-            public TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T> Use<TMethod2, TMethod>(global::System.Func<TMethod2, bool> first, global::System.Func<TMethod, bool> second)
+            public TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T> Use<TMethod2, TMethod>(global::System.Func<TMethod2, bool>? first, global::System.Func<TMethod, bool>? second)
             {
-                global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_first = first;
-                global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_second = second;
+                global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_first = first is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod2>(default(TMethod2)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod2>)first;
+                global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_second = second is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod>(default(TMethod)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod>)second;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_first.Matcher, __fa_second.Matcher };
                 return new TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Use", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2, TMethod>.Value);
             }
@@ -1560,24 +1560,24 @@ namespace TUnit.Mocks.Generated
                 return new TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Use", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2, TMethod>.Value);
             }
 
-            public TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T> Use<TMethod2, TMethod>(global::System.Func<TMethod2, bool> first, global::TUnit.Mocks.Arguments.Arg<TMethod> second)
+            public TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T> Use<TMethod2, TMethod>(global::System.Func<TMethod2, bool>? first, global::TUnit.Mocks.Arguments.Arg<TMethod> second)
             {
-                global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_first = first;
+                global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_first = first is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod2>(default(TMethod2)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod2>)first;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_first.Matcher, second.Matcher };
                 return new TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Use", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2, TMethod>.Value);
             }
 
-            public TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T> Use<TMethod2, TMethod>(global::TUnit.Mocks.Arguments.Arg<TMethod2> first, global::System.Func<TMethod, bool> second)
+            public TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T> Use<TMethod2, TMethod>(global::TUnit.Mocks.Arguments.Arg<TMethod2> first, global::System.Func<TMethod, bool>? second)
             {
-                global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_second = second;
+                global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_second = second is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod>(default(TMethod)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod>)second;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { first.Matcher, __fa_second.Matcher };
                 return new TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Use", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2, TMethod>.Value);
             }
 
-            public TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T> Use<TMethod2, TMethod>(global::System.Func<TMethod2, bool> first, global::System.Func<TMethod, bool> second)
+            public TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T> Use<TMethod2, TMethod>(global::System.Func<TMethod2, bool>? first, global::System.Func<TMethod, bool>? second)
             {
-                global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_first = first;
-                global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_second = second;
+                global::TUnit.Mocks.Arguments.Arg<TMethod2> __fa_first = first is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod2>(default(TMethod2)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod2>)first;
+                global::TUnit.Mocks.Arguments.Arg<TMethod> __fa_second = second is null ? global::TUnit.Mocks.Arguments.Arg.Is<TMethod>(default(TMethod)!) : (global::TUnit.Mocks.Arguments.Arg<TMethod>)second;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_first.Matcher, __fa_second.Matcher };
                 return new TestNamespace_ITaken_T__Use_M0_MockCall<TMethod2, TMethod, T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Use", matchers, global::TUnit.Mocks.TypeArguments.Of<TMethod2, TMethod>.Value);
             }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Conflict_With_Existing_Type_Falls_Back_To_Generated_Namespace.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Conflict_With_Existing_Type_Falls_Back_To_Generated_Namespace.verified.txt
index ea9417cfc6..cbe0512812 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Conflict_With_Existing_Type_Falls_Back_To_Generated_Namespace.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Conflict_With_Existing_Type_Falls_Back_To_Generated_Namespace.verified.txt
@@ -93,9 +93,9 @@ namespace TUnit.Mocks.Generated
             return new MyApp_IGreeter_Greet_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Greet", matchers);
         }
 
-        public static MyApp_IGreeter_Greet_M0_MockCall Greet(this global::TUnit.Mocks.Mock<global::MyApp.IGreeter> mock, global::System.Func<string, bool> name)
+        public static MyApp_IGreeter_Greet_M0_MockCall Greet(this global::TUnit.Mocks.Mock<global::MyApp.IGreeter> mock, global::System.Func<string, bool>? name)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_name = name;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_name = name is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)name;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_name.Matcher };
             return new MyApp_IGreeter_Greet_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Greet", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Delegates_Returning_Task_And_ValueTask.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Delegates_Returning_Task_And_ValueTask.verified.txt
index 40893341e9..51df504ff5 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Delegates_Returning_Task_And_ValueTask.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Delegates_Returning_Task_And_ValueTask.verified.txt
@@ -180,9 +180,9 @@ namespace TUnit.Mocks.Generated
             return new System_Func_int_System_Threading_Tasks_Task__Invoke_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Invoke", matchers);
         }
 
-        public static System_Func_int_System_Threading_Tasks_Task__Invoke_M0_MockCall Invoke(this global::TUnit.Mocks.Mock<global::System.Func<int, global::System.Threading.Tasks.Task>> mock, global::System.Func<int, bool> arg)
+        public static System_Func_int_System_Threading_Tasks_Task__Invoke_M0_MockCall Invoke(this global::TUnit.Mocks.Mock<global::System.Func<int, global::System.Threading.Tasks.Task>> mock, global::System.Func<int, bool>? arg)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_arg = arg;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_arg = arg is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)arg;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_arg.Matcher };
             return new System_Func_int_System_Threading_Tasks_Task__Invoke_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Invoke", matchers);
         }
@@ -329,9 +329,9 @@ namespace TUnit.Mocks.Generated
             return new System_Func_int_System_Threading_Tasks_Task_int__Invoke_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Invoke", matchers);
         }
 
-        public static System_Func_int_System_Threading_Tasks_Task_int__Invoke_M0_MockCall Invoke(this global::TUnit.Mocks.Mock<global::System.Func<int, global::System.Threading.Tasks.Task<int>>> mock, global::System.Func<int, bool> arg)
+        public static System_Func_int_System_Threading_Tasks_Task_int__Invoke_M0_MockCall Invoke(this global::TUnit.Mocks.Mock<global::System.Func<int, global::System.Threading.Tasks.Task<int>>> mock, global::System.Func<int, bool>? arg)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_arg = arg;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_arg = arg is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)arg;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_arg.Matcher };
             return new System_Func_int_System_Threading_Tasks_Task_int__Invoke_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Invoke", matchers);
         }
@@ -533,9 +533,9 @@ namespace TUnit.Mocks.Generated
             return new System_Func_string_System_Threading_Tasks_ValueTask_string__Invoke_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Invoke", matchers);
         }
 
-        public static System_Func_string_System_Threading_Tasks_ValueTask_string__Invoke_M0_MockCall Invoke(this global::TUnit.Mocks.Mock<global::System.Func<string, global::System.Threading.Tasks.ValueTask<string>>> mock, global::System.Func<string, bool> arg)
+        public static System_Func_string_System_Threading_Tasks_ValueTask_string__Invoke_M0_MockCall Invoke(this global::TUnit.Mocks.Mock<global::System.Func<string, global::System.Threading.Tasks.ValueTask<string>>> mock, global::System.Func<string, bool>? arg)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg = arg;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg = arg is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)arg;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_arg.Matcher };
             return new System_Func_string_System_Threading_Tasks_ValueTask_string__Invoke_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Invoke", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/External_Interface_With_Indexer_Static_Extension_Discovery.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/External_Interface_With_Indexer_Static_Extension_Discovery.verified.txt
index c149d5c5d5..118e3e1623 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/External_Interface_With_Indexer_Static_Extension_Discovery.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/External_Interface_With_Indexer_Static_Extension_Discovery.verified.txt
@@ -101,9 +101,9 @@ namespace TUnit.Mocks.Generated
             return new Microsoft_Extensions_Configuration_IConfiguration_GetSectionValue_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "GetSectionValue", matchers);
         }
 
-        public static Microsoft_Extensions_Configuration_IConfiguration_GetSectionValue_M0_MockCall GetSectionValue(this global::TUnit.Mocks.Mock<global::Microsoft.Extensions.Configuration.IConfiguration> mock, global::System.Func<string, bool> key)
+        public static Microsoft_Extensions_Configuration_IConfiguration_GetSectionValue_M0_MockCall GetSectionValue(this global::TUnit.Mocks.Mock<global::Microsoft.Extensions.Configuration.IConfiguration> mock, global::System.Func<string, bool>? key)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_key = key;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_key = key is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)key;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_key.Matcher };
             return new Microsoft_Extensions_Configuration_IConfiguration_GetSectionValue_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "GetSectionValue", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Generic_Constraints_Preserve_Nullability.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Generic_Constraints_Preserve_Nullability.verified.txt
index a9418dba92..7fe81a758f 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Generic_Constraints_Preserve_Nullability.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Generic_Constraints_Preserve_Nullability.verified.txt
@@ -128,9 +128,9 @@ namespace TUnit.Mocks.Generated
             return new IService_Get_M0_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Get", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
 
-        public static IService_Get_M0_MockCall<T> Get<T>(this global::TUnit.Mocks.Mock<global::IService> mock, global::System.Func<string, bool> key) where T : class?
+        public static IService_Get_M0_MockCall<T> Get<T>(this global::TUnit.Mocks.Mock<global::IService> mock, global::System.Func<string, bool>? key) where T : class?
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_key = key;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_key = key is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)key;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_key.Matcher };
             return new IService_Get_M0_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Get", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Generic_Interface_Extension_Discovery.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Generic_Interface_Extension_Discovery.verified.txt
index 19f555ee3f..660331fa99 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Generic_Interface_Extension_Discovery.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Generic_Interface_Extension_Discovery.verified.txt
@@ -91,9 +91,9 @@ namespace TUnit.Mocks.Generated
             return new IRepository_T__GetById_M0_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "GetById", matchers);
         }
 
-        public static IRepository_T__GetById_M0_MockCall<T> GetById<T>(this global::TUnit.Mocks.Mock<global::IRepository<T>> mock, global::System.Func<int, bool> id)
+        public static IRepository_T__GetById_M0_MockCall<T> GetById<T>(this global::TUnit.Mocks.Mock<global::IRepository<T>> mock, global::System.Func<int, bool>? id)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_id = id;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_id = id is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)id;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_id.Matcher };
             return new IRepository_T__GetById_M0_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "GetById", matchers);
         }
@@ -104,9 +104,9 @@ namespace TUnit.Mocks.Generated
             return new IRepository_T__Save_M1_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Save", matchers);
         }
 
-        public static IRepository_T__Save_M1_MockCall<T> Save<T>(this global::TUnit.Mocks.Mock<global::IRepository<T>> mock, global::System.Func<T, bool> entity)
+        public static IRepository_T__Save_M1_MockCall<T> Save<T>(this global::TUnit.Mocks.Mock<global::IRepository<T>> mock, global::System.Func<T, bool>? entity)
         {
-            global::TUnit.Mocks.Arguments.Arg<T> __fa_entity = entity;
+            global::TUnit.Mocks.Arguments.Arg<T> __fa_entity = entity is null ? global::TUnit.Mocks.Arguments.Arg.Is<T>(default(T)!) : (global::TUnit.Mocks.Arguments.Arg<T>)entity;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_entity.Matcher };
             return new IRepository_T__Save_M1_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Save", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Generic_Interface_With_Class_Type_Argument.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Generic_Interface_With_Class_Type_Argument.verified.txt
index fbd4c2a39c..1d71364fc0 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Generic_Interface_With_Class_Type_Argument.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Generic_Interface_With_Class_Type_Argument.verified.txt
@@ -97,9 +97,9 @@ namespace TUnit.Mocks.Generated
             return new Sandbox_IFoo_T__Process_M1_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Process", matchers);
         }
 
-        public static Sandbox_IFoo_T__Process_M1_MockCall<T> Process<T>(this global::TUnit.Mocks.Mock<global::Sandbox.IFoo<T>> mock, global::System.Func<T, bool> item)
+        public static Sandbox_IFoo_T__Process_M1_MockCall<T> Process<T>(this global::TUnit.Mocks.Mock<global::Sandbox.IFoo<T>> mock, global::System.Func<T, bool>? item)
         {
-            global::TUnit.Mocks.Arguments.Arg<T> __fa_item = item;
+            global::TUnit.Mocks.Arguments.Arg<T> __fa_item = item is null ? global::TUnit.Mocks.Arguments.Arg.Is<T>(default(T)!) : (global::TUnit.Mocks.Arguments.Arg<T>)item;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_item.Matcher };
             return new Sandbox_IFoo_T__Process_M1_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Process", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Generic_Interface_With_Multiple_Non_Builtin_Type_Arguments.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Generic_Interface_With_Multiple_Non_Builtin_Type_Arguments.verified.txt
index b5ec65ba88..5f6fb67879 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Generic_Interface_With_Multiple_Non_Builtin_Type_Arguments.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Generic_Interface_With_Multiple_Non_Builtin_Type_Arguments.verified.txt
@@ -87,9 +87,9 @@ namespace TUnit.Mocks.Generated
             return new Sandbox_IMapper_TIn_TOut__Map_M0_MockCall<TIn, TOut>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Map", matchers);
         }
 
-        public static Sandbox_IMapper_TIn_TOut__Map_M0_MockCall<TIn, TOut> Map<TIn, TOut>(this global::TUnit.Mocks.Mock<global::Sandbox.IMapper<TIn, TOut>> mock, global::System.Func<TIn, bool> input)
+        public static Sandbox_IMapper_TIn_TOut__Map_M0_MockCall<TIn, TOut> Map<TIn, TOut>(this global::TUnit.Mocks.Mock<global::Sandbox.IMapper<TIn, TOut>> mock, global::System.Func<TIn, bool>? input)
         {
-            global::TUnit.Mocks.Arguments.Arg<TIn> __fa_input = input;
+            global::TUnit.Mocks.Arguments.Arg<TIn> __fa_input = input is null ? global::TUnit.Mocks.Arguments.Arg.Is<TIn>(default(TIn)!) : (global::TUnit.Mocks.Arguments.Arg<TIn>)input;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_input.Matcher };
             return new Sandbox_IMapper_TIn_TOut__Map_M0_MockCall<TIn, TOut>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Map", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Generic_Interface_With_Nested_Namespace_Type_Argument.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Generic_Interface_With_Nested_Namespace_Type_Argument.verified.txt
index 2d89e17c18..4b51a73dcc 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Generic_Interface_With_Nested_Namespace_Type_Argument.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Generic_Interface_With_Nested_Namespace_Type_Argument.verified.txt
@@ -103,9 +103,9 @@ namespace TUnit.Mocks.Generated
             return new Sandbox_IService_T__Apply_M1_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Apply", matchers);
         }
 
-        public static Sandbox_IService_T__Apply_M1_MockCall<T> Apply<T>(this global::TUnit.Mocks.Mock<global::Sandbox.IService<T>> mock, global::System.Func<T, bool> config)
+        public static Sandbox_IService_T__Apply_M1_MockCall<T> Apply<T>(this global::TUnit.Mocks.Mock<global::Sandbox.IService<T>> mock, global::System.Func<T, bool>? config)
         {
-            global::TUnit.Mocks.Arguments.Arg<T> __fa_config = config;
+            global::TUnit.Mocks.Arguments.Arg<T> __fa_config = config is null ? global::TUnit.Mocks.Arguments.Arg.Is<T>(default(T)!) : (global::TUnit.Mocks.Arguments.Arg<T>)config;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_config.Matcher };
             return new Sandbox_IService_T__Apply_M1_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Apply", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_Directly_Inheriting_IEnumerable.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_Directly_Inheriting_IEnumerable.verified.txt
index 73f5c0b383..e5731dc259 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_Directly_Inheriting_IEnumerable.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_Directly_Inheriting_IEnumerable.verified.txt
@@ -108,9 +108,9 @@ namespace TUnit.Mocks.Generated
             return new ICustomCollection_Add_M1_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Add", matchers);
         }
 
-        public static ICustomCollection_Add_M1_MockCall Add(this global::TUnit.Mocks.Mock<global::ICustomCollection> mock, global::System.Func<int, bool> item)
+        public static ICustomCollection_Add_M1_MockCall Add(this global::TUnit.Mocks.Mock<global::ICustomCollection> mock, global::System.Func<int, bool>? item)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_item = item;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_item = item is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)item;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_item.Matcher };
             return new ICustomCollection_Add_M1_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Add", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_FluentUI_Shape_Nullable_Warnings.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_FluentUI_Shape_Nullable_Warnings.verified.txt
index 0ab01f43d0..84447f00e5 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_FluentUI_Shape_Nullable_Warnings.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_FluentUI_Shape_Nullable_Warnings.verified.txt
@@ -404,24 +404,24 @@ namespace TUnit.Mocks.Generated
             return new IDialogService_UpdateDialogAsync_M0_MockCall<TData>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "UpdateDialogAsync", matchers, global::TUnit.Mocks.TypeArguments.Of<TData>.Value);
         }
 
-        public static IDialogService_UpdateDialogAsync_M0_MockCall<TData> UpdateDialogAsync<TData>(this global::TUnit.Mocks.Mock<global::IDialogService> mock, global::System.Func<string, bool> id, global::TUnit.Mocks.Arguments.Arg<global::DialogParameters<TData>> parameters) where TData : class
+        public static IDialogService_UpdateDialogAsync_M0_MockCall<TData> UpdateDialogAsync<TData>(this global::TUnit.Mocks.Mock<global::IDialogService> mock, global::System.Func<string, bool>? id, global::TUnit.Mocks.Arguments.Arg<global::DialogParameters<TData>> parameters) where TData : class
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_id = id;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_id = id is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)id;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_id.Matcher, parameters.Matcher };
             return new IDialogService_UpdateDialogAsync_M0_MockCall<TData>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "UpdateDialogAsync", matchers, global::TUnit.Mocks.TypeArguments.Of<TData>.Value);
         }
 
-        public static IDialogService_UpdateDialogAsync_M0_MockCall<TData> UpdateDialogAsync<TData>(this global::TUnit.Mocks.Mock<global::IDialogService> mock, global::TUnit.Mocks.Arguments.Arg<string> id, global::System.Func<global::DialogParameters<TData>, bool> parameters) where TData : class
+        public static IDialogService_UpdateDialogAsync_M0_MockCall<TData> UpdateDialogAsync<TData>(this global::TUnit.Mocks.Mock<global::IDialogService> mock, global::TUnit.Mocks.Arguments.Arg<string> id, global::System.Func<global::DialogParameters<TData>, bool>? parameters) where TData : class
         {
-            global::TUnit.Mocks.Arguments.Arg<global::DialogParameters<TData>> __fa_parameters = parameters;
+            global::TUnit.Mocks.Arguments.Arg<global::DialogParameters<TData>> __fa_parameters = parameters is null ? global::TUnit.Mocks.Arguments.Arg.Is<global::DialogParameters<TData>>(default(global::DialogParameters<TData>)!) : (global::TUnit.Mocks.Arguments.Arg<global::DialogParameters<TData>>)parameters;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { id.Matcher, __fa_parameters.Matcher };
             return new IDialogService_UpdateDialogAsync_M0_MockCall<TData>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "UpdateDialogAsync", matchers, global::TUnit.Mocks.TypeArguments.Of<TData>.Value);
         }
 
-        public static IDialogService_UpdateDialogAsync_M0_MockCall<TData> UpdateDialogAsync<TData>(this global::TUnit.Mocks.Mock<global::IDialogService> mock, global::System.Func<string, bool> id, global::System.Func<global::DialogParameters<TData>, bool> parameters) where TData : class
+        public static IDialogService_UpdateDialogAsync_M0_MockCall<TData> UpdateDialogAsync<TData>(this global::TUnit.Mocks.Mock<global::IDialogService> mock, global::System.Func<string, bool>? id, global::System.Func<global::DialogParameters<TData>, bool>? parameters) where TData : class
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_id = id;
-            global::TUnit.Mocks.Arguments.Arg<global::DialogParameters<TData>> __fa_parameters = parameters;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_id = id is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)id;
+            global::TUnit.Mocks.Arguments.Arg<global::DialogParameters<TData>> __fa_parameters = parameters is null ? global::TUnit.Mocks.Arguments.Arg.Is<global::DialogParameters<TData>>(default(global::DialogParameters<TData>)!) : (global::TUnit.Mocks.Arguments.Arg<global::DialogParameters<TData>>)parameters;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_id.Matcher, __fa_parameters.Matcher };
             return new IDialogService_UpdateDialogAsync_M0_MockCall<TData>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "UpdateDialogAsync", matchers, global::TUnit.Mocks.TypeArguments.Of<TData>.Value);
         }
@@ -432,24 +432,24 @@ namespace TUnit.Mocks.Generated
             return new IDialogService_ShowDialogAsync_M1_MockCall<TDialog>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "ShowDialogAsync", matchers, global::TUnit.Mocks.TypeArguments.Of<TDialog>.Value);
         }
 
-        public static IDialogService_ShowDialogAsync_M1_MockCall<TDialog> ShowDialogAsync<TDialog>(this global::TUnit.Mocks.Mock<global::IDialogService> mock, global::System.Func<object, bool> data, global::TUnit.Mocks.Arguments.Arg<global::DialogParameters> parameters) where TDialog : global::IDialogContentComponent
+        public static IDialogService_ShowDialogAsync_M1_MockCall<TDialog> ShowDialogAsync<TDialog>(this global::TUnit.Mocks.Mock<global::IDialogService> mock, global::System.Func<object, bool>? data, global::TUnit.Mocks.Arguments.Arg<global::DialogParameters> parameters) where TDialog : global::IDialogContentComponent
         {
-            global::TUnit.Mocks.Arguments.Arg<object> __fa_data = data;
+            global::TUnit.Mocks.Arguments.Arg<object> __fa_data = data is null ? global::TUnit.Mocks.Arguments.Arg.Is<object>(default(object)!) : (global::TUnit.Mocks.Arguments.Arg<object>)data;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_data.Matcher, parameters.Matcher };
             return new IDialogService_ShowDialogAsync_M1_MockCall<TDialog>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "ShowDialogAsync", matchers, global::TUnit.Mocks.TypeArguments.Of<TDialog>.Value);
         }
 
-        public static IDialogService_ShowDialogAsync_M1_MockCall<TDialog> ShowDialogAsync<TDialog>(this global::TUnit.Mocks.Mock<global::IDialogService> mock, global::TUnit.Mocks.Arguments.Arg<object> data, global::System.Func<global::DialogParameters, bool> parameters) where TDialog : global::IDialogContentComponent
+        public static IDialogService_ShowDialogAsync_M1_MockCall<TDialog> ShowDialogAsync<TDialog>(this global::TUnit.Mocks.Mock<global::IDialogService> mock, global::TUnit.Mocks.Arguments.Arg<object> data, global::System.Func<global::DialogParameters, bool>? parameters) where TDialog : global::IDialogContentComponent
         {
-            global::TUnit.Mocks.Arguments.Arg<global::DialogParameters> __fa_parameters = parameters;
+            global::TUnit.Mocks.Arguments.Arg<global::DialogParameters> __fa_parameters = parameters is null ? global::TUnit.Mocks.Arguments.Arg.Is<global::DialogParameters>(default(global::DialogParameters)!) : (global::TUnit.Mocks.Arguments.Arg<global::DialogParameters>)parameters;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { data.Matcher, __fa_parameters.Matcher };
             return new IDialogService_ShowDialogAsync_M1_MockCall<TDialog>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "ShowDialogAsync", matchers, global::TUnit.Mocks.TypeArguments.Of<TDialog>.Value);
         }
 
-        public static IDialogService_ShowDialogAsync_M1_MockCall<TDialog> ShowDialogAsync<TDialog>(this global::TUnit.Mocks.Mock<global::IDialogService> mock, global::System.Func<object, bool> data, global::System.Func<global::DialogParameters, bool> parameters) where TDialog : global::IDialogContentComponent
+        public static IDialogService_ShowDialogAsync_M1_MockCall<TDialog> ShowDialogAsync<TDialog>(this global::TUnit.Mocks.Mock<global::IDialogService> mock, global::System.Func<object, bool>? data, global::System.Func<global::DialogParameters, bool>? parameters) where TDialog : global::IDialogContentComponent
         {
-            global::TUnit.Mocks.Arguments.Arg<object> __fa_data = data;
-            global::TUnit.Mocks.Arguments.Arg<global::DialogParameters> __fa_parameters = parameters;
+            global::TUnit.Mocks.Arguments.Arg<object> __fa_data = data is null ? global::TUnit.Mocks.Arguments.Arg.Is<object>(default(object)!) : (global::TUnit.Mocks.Arguments.Arg<object>)data;
+            global::TUnit.Mocks.Arguments.Arg<global::DialogParameters> __fa_parameters = parameters is null ? global::TUnit.Mocks.Arguments.Arg.Is<global::DialogParameters>(default(global::DialogParameters)!) : (global::TUnit.Mocks.Arguments.Arg<global::DialogParameters>)parameters;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_data.Matcher, __fa_parameters.Matcher };
             return new IDialogService_ShowDialogAsync_M1_MockCall<TDialog>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "ShowDialogAsync", matchers, global::TUnit.Mocks.TypeArguments.Of<TDialog>.Value);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_Inheriting_Multiple_Interfaces.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_Inheriting_Multiple_Interfaces.verified.txt
index 4f98fb9104..aa87c9721b 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_Inheriting_Multiple_Interfaces.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_Inheriting_Multiple_Interfaces.verified.txt
@@ -119,9 +119,9 @@ namespace TUnit.Mocks.Generated
             return new IReadWriter_Write_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Write", matchers);
         }
 
-        public static IReadWriter_Write_M2_MockCall Write(this global::TUnit.Mocks.Mock<global::IReadWriter> mock, global::System.Func<string, bool> data)
+        public static IReadWriter_Write_M2_MockCall Write(this global::TUnit.Mocks.Mock<global::IReadWriter> mock, global::System.Func<string, bool>? data)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_data = data;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_data = data is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)data;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_data.Matcher };
             return new IReadWriter_Write_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Write", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Async_Methods.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Async_Methods.verified.txt
index 10c01de76a..39c22b9d68 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Async_Methods.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Async_Methods.verified.txt
@@ -160,9 +160,9 @@ namespace TUnit.Mocks.Generated
             return new IAsyncService_GetValueAsync_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "GetValueAsync", matchers);
         }
 
-        public static IAsyncService_GetValueAsync_M0_MockCall GetValueAsync(this global::TUnit.Mocks.Mock<global::IAsyncService> mock, global::System.Func<string, bool> key)
+        public static IAsyncService_GetValueAsync_M0_MockCall GetValueAsync(this global::TUnit.Mocks.Mock<global::IAsyncService> mock, global::System.Func<string, bool>? key)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_key = key;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_key = key is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)key;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_key.Matcher };
             return new IAsyncService_GetValueAsync_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "GetValueAsync", matchers);
         }
@@ -179,9 +179,9 @@ namespace TUnit.Mocks.Generated
             return new IAsyncService_ComputeAsync_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "ComputeAsync", matchers);
         }
 
-        public static IAsyncService_ComputeAsync_M2_MockCall ComputeAsync(this global::TUnit.Mocks.Mock<global::IAsyncService> mock, global::System.Func<int, bool> input)
+        public static IAsyncService_ComputeAsync_M2_MockCall ComputeAsync(this global::TUnit.Mocks.Mock<global::IAsyncService> mock, global::System.Func<int, bool>? input)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_input = input;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_input = input is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)input;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_input.Matcher };
             return new IAsyncService_ComputeAsync_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "ComputeAsync", matchers);
         }
@@ -192,9 +192,9 @@ namespace TUnit.Mocks.Generated
             return new IAsyncService_InitializeAsync_M3_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "InitializeAsync", matchers);
         }
 
-        public static IAsyncService_InitializeAsync_M3_MockCall InitializeAsync(this global::TUnit.Mocks.Mock<global::IAsyncService> mock, global::System.Func<global::System.Threading.CancellationToken, bool> ct)
+        public static IAsyncService_InitializeAsync_M3_MockCall InitializeAsync(this global::TUnit.Mocks.Mock<global::IAsyncService> mock, global::System.Func<global::System.Threading.CancellationToken, bool>? ct)
         {
-            global::TUnit.Mocks.Arguments.Arg<global::System.Threading.CancellationToken> __fa_ct = ct;
+            global::TUnit.Mocks.Arguments.Arg<global::System.Threading.CancellationToken> __fa_ct = ct is null ? global::TUnit.Mocks.Arguments.Arg.Is<global::System.Threading.CancellationToken>(default(global::System.Threading.CancellationToken)!) : (global::TUnit.Mocks.Arguments.Arg<global::System.Threading.CancellationToken>)ct;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_ct.Matcher };
             return new IAsyncService_InitializeAsync_M3_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "InitializeAsync", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Enum_And_Defaultable_Generic_Async_Results.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Enum_And_Defaultable_Generic_Async_Results.verified.txt
index 23d0227543..742d5de13e 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Enum_And_Defaultable_Generic_Async_Results.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Enum_And_Defaultable_Generic_Async_Results.verified.txt
@@ -172,9 +172,9 @@ namespace TUnit.Mocks.Generated
             return new IEnumAndGenericService_FindAsync_M2_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "FindAsync", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
 
-        public static IEnumAndGenericService_FindAsync_M2_MockCall<T> FindAsync<T>(this global::TUnit.Mocks.Mock<global::IEnumAndGenericService> mock, global::System.Func<int, bool> id)
+        public static IEnumAndGenericService_FindAsync_M2_MockCall<T> FindAsync<T>(this global::TUnit.Mocks.Mock<global::IEnumAndGenericService> mock, global::System.Func<int, bool>? id)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_id = id;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_id = id is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)id;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_id.Matcher };
             return new IEnumAndGenericService_FindAsync_M2_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "FindAsync", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
@@ -185,9 +185,9 @@ namespace TUnit.Mocks.Generated
             return new IEnumAndGenericService_FindStructAsync_M3_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "FindStructAsync", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
 
-        public static IEnumAndGenericService_FindStructAsync_M3_MockCall<T> FindStructAsync<T>(this global::TUnit.Mocks.Mock<global::IEnumAndGenericService> mock, global::System.Func<int, bool> id) where T : struct
+        public static IEnumAndGenericService_FindStructAsync_M3_MockCall<T> FindStructAsync<T>(this global::TUnit.Mocks.Mock<global::IEnumAndGenericService> mock, global::System.Func<int, bool>? id) where T : struct
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_id = id;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_id = id is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)id;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_id.Matcher };
             return new IEnumAndGenericService_FindStructAsync_M3_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "FindStructAsync", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Events.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Events.verified.txt
index 2e26955ac8..b508e33e41 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Events.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Events.verified.txt
@@ -147,9 +147,9 @@ namespace TUnit.Mocks.Generated
             return new INotifier_Notify_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Notify", matchers);
         }
 
-        public static INotifier_Notify_M0_MockCall Notify(this global::TUnit.Mocks.Mock<global::INotifier> mock, global::System.Func<string, bool> message)
+        public static INotifier_Notify_M0_MockCall Notify(this global::TUnit.Mocks.Mock<global::INotifier> mock, global::System.Func<string, bool>? message)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_message = message;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_message = message is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)message;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_message.Matcher };
             return new INotifier_Notify_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Notify", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Generic_Method_Constraints_On_Explicit_Impl.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Generic_Method_Constraints_On_Explicit_Impl.verified.txt
index 3cccac4a53..0c9609694b 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Generic_Method_Constraints_On_Explicit_Impl.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Generic_Method_Constraints_On_Explicit_Impl.verified.txt
@@ -122,9 +122,9 @@ namespace TUnit.Mocks.Generated
             return new IConstrained_GetNotnull_M0_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "GetNotnull", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
 
-        public static IConstrained_GetNotnull_M0_MockCall<T> GetNotnull<T>(this global::TUnit.Mocks.Mock<global::IConstrained> mock, global::System.Func<string, bool> key) where T : notnull
+        public static IConstrained_GetNotnull_M0_MockCall<T> GetNotnull<T>(this global::TUnit.Mocks.Mock<global::IConstrained> mock, global::System.Func<string, bool>? key) where T : notnull
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_key = key;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_key = key is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)key;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_key.Matcher };
             return new IConstrained_GetNotnull_M0_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "GetNotnull", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Generic_Methods.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Generic_Methods.verified.txt
index bec55bab71..c1ff07baff 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Generic_Methods.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Generic_Methods.verified.txt
@@ -104,9 +104,9 @@ namespace TUnit.Mocks.Generated
             return new IRepository_GetById_M0_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "GetById", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
 
-        public static IRepository_GetById_M0_MockCall<T> GetById<T>(this global::TUnit.Mocks.Mock<global::IRepository> mock, global::System.Func<int, bool> id) where T : class
+        public static IRepository_GetById_M0_MockCall<T> GetById<T>(this global::TUnit.Mocks.Mock<global::IRepository> mock, global::System.Func<int, bool>? id) where T : class
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_id = id;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_id = id is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)id;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_id.Matcher };
             return new IRepository_GetById_M0_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "GetById", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
@@ -117,9 +117,9 @@ namespace TUnit.Mocks.Generated
             return new IRepository_Save_M1_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Save", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
 
-        public static IRepository_Save_M1_MockCall<T> Save<T>(this global::TUnit.Mocks.Mock<global::IRepository> mock, global::System.Func<T, bool> entity) where T : class, new()
+        public static IRepository_Save_M1_MockCall<T> Save<T>(this global::TUnit.Mocks.Mock<global::IRepository> mock, global::System.Func<T, bool>? entity) where T : class, new()
         {
-            global::TUnit.Mocks.Arguments.Arg<T> __fa_entity = entity;
+            global::TUnit.Mocks.Arguments.Arg<T> __fa_entity = entity is null ? global::TUnit.Mocks.Arguments.Arg.Is<T>(default(T)!) : (global::TUnit.Mocks.Arguments.Arg<T>)entity;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_entity.Matcher };
             return new IRepository_Save_M1_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Save", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
@@ -130,9 +130,9 @@ namespace TUnit.Mocks.Generated
             return new IRepository_Transform_M2_MockCall<TInput, TResult>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Transform", matchers, global::TUnit.Mocks.TypeArguments.Of<TInput, TResult>.Value);
         }
 
-        public static IRepository_Transform_M2_MockCall<TInput, TResult> Transform<TInput, TResult>(this global::TUnit.Mocks.Mock<global::IRepository> mock, global::System.Func<TInput, bool> input) where TInput : notnull where TResult : struct
+        public static IRepository_Transform_M2_MockCall<TInput, TResult> Transform<TInput, TResult>(this global::TUnit.Mocks.Mock<global::IRepository> mock, global::System.Func<TInput, bool>? input) where TInput : notnull where TResult : struct
         {
-            global::TUnit.Mocks.Arguments.Arg<TInput> __fa_input = input;
+            global::TUnit.Mocks.Arguments.Arg<TInput> __fa_input = input is null ? global::TUnit.Mocks.Arguments.Arg.Is<TInput>(default(TInput)!) : (global::TUnit.Mocks.Arguments.Arg<TInput>)input;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_input.Matcher };
             return new IRepository_Transform_M2_MockCall<TInput, TResult>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Transform", matchers, global::TUnit.Mocks.TypeArguments.Of<TInput, TResult>.Value);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Keyword_Member_Names.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Keyword_Member_Names.verified.txt
index 587632cdee..3b937d5f35 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Keyword_Member_Names.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Keyword_Member_Names.verified.txt
@@ -117,9 +117,9 @@ namespace TUnit.Mocks.Generated
             return new IEscapedNames_event_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "event", matchers);
         }
 
-        public static IEscapedNames_event_M2_MockCall @event(this global::TUnit.Mocks.Mock<global::IEscapedNames> mock, global::System.Func<int, bool> @params)
+        public static IEscapedNames_event_M2_MockCall @event(this global::TUnit.Mocks.Mock<global::IEscapedNames> mock, global::System.Func<int, bool>? @params)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_params = @params;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_params = @params is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)@params;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_params.Matcher };
             return new IEscapedNames_event_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "event", matchers);
         }
@@ -130,24 +130,24 @@ namespace TUnit.Mocks.Generated
             return new IEscapedNames_namespace_M3_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "namespace", matchers);
         }
 
-        public static IEscapedNames_namespace_M3_MockCall @namespace(this global::TUnit.Mocks.Mock<global::IEscapedNames> mock, global::System.Func<int, bool> @new, global::TUnit.Mocks.Arguments.Arg<int> @static)
+        public static IEscapedNames_namespace_M3_MockCall @namespace(this global::TUnit.Mocks.Mock<global::IEscapedNames> mock, global::System.Func<int, bool>? @new, global::TUnit.Mocks.Arguments.Arg<int> @static)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_new = @new;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_new = @new is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)@new;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_new.Matcher, @static.Matcher };
             return new IEscapedNames_namespace_M3_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "namespace", matchers);
         }
 
-        public static IEscapedNames_namespace_M3_MockCall @namespace(this global::TUnit.Mocks.Mock<global::IEscapedNames> mock, global::TUnit.Mocks.Arguments.Arg<int> @new, global::System.Func<int, bool> @static)
+        public static IEscapedNames_namespace_M3_MockCall @namespace(this global::TUnit.Mocks.Mock<global::IEscapedNames> mock, global::TUnit.Mocks.Arguments.Arg<int> @new, global::System.Func<int, bool>? @static)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_static = @static;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_static = @static is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)@static;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { @new.Matcher, __fa_static.Matcher };
             return new IEscapedNames_namespace_M3_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "namespace", matchers);
         }
 
-        public static IEscapedNames_namespace_M3_MockCall @namespace(this global::TUnit.Mocks.Mock<global::IEscapedNames> mock, global::System.Func<int, bool> @new, global::System.Func<int, bool> @static)
+        public static IEscapedNames_namespace_M3_MockCall @namespace(this global::TUnit.Mocks.Mock<global::IEscapedNames> mock, global::System.Func<int, bool>? @new, global::System.Func<int, bool>? @static)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_new = @new;
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_static = @static;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_new = @new is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)@new;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_static = @static is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)@static;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_new.Matcher, __fa_static.Matcher };
             return new IEscapedNames_namespace_M3_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "namespace", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Keyword_Parameter_Names.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Keyword_Parameter_Names.verified.txt
index d8172ce4c6..940b883e5d 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Keyword_Parameter_Names.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Keyword_Parameter_Names.verified.txt
@@ -97,9 +97,9 @@ namespace TUnit.Mocks.Generated
             return new ITest_Test_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Test", matchers);
         }
 
-        public static ITest_Test_M0_MockCall Test(this global::TUnit.Mocks.Mock<global::ITest> mock, global::System.Func<string, bool> @event)
+        public static ITest_Test_M0_MockCall Test(this global::TUnit.Mocks.Mock<global::ITest> mock, global::System.Func<string, bool>? @event)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_event = @event;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_event = @event is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)@event;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_event.Matcher };
             return new ITest_Test_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Test", matchers);
         }
@@ -110,24 +110,24 @@ namespace TUnit.Mocks.Generated
             return new ITest_Get_M1_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Get", matchers);
         }
 
-        public static ITest_Get_M1_MockCall Get(this global::TUnit.Mocks.Mock<global::ITest> mock, global::System.Func<int, bool> @class, global::TUnit.Mocks.Arguments.Arg<string> @return)
+        public static ITest_Get_M1_MockCall Get(this global::TUnit.Mocks.Mock<global::ITest> mock, global::System.Func<int, bool>? @class, global::TUnit.Mocks.Arguments.Arg<string> @return)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_class = @class;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_class = @class is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)@class;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_class.Matcher, @return.Matcher };
             return new ITest_Get_M1_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Get", matchers);
         }
 
-        public static ITest_Get_M1_MockCall Get(this global::TUnit.Mocks.Mock<global::ITest> mock, global::TUnit.Mocks.Arguments.Arg<int> @class, global::System.Func<string, bool> @return)
+        public static ITest_Get_M1_MockCall Get(this global::TUnit.Mocks.Mock<global::ITest> mock, global::TUnit.Mocks.Arguments.Arg<int> @class, global::System.Func<string, bool>? @return)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_return = @return;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_return = @return is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)@return;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { @class.Matcher, __fa_return.Matcher };
             return new ITest_Get_M1_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Get", matchers);
         }
 
-        public static ITest_Get_M1_MockCall Get(this global::TUnit.Mocks.Mock<global::ITest> mock, global::System.Func<int, bool> @class, global::System.Func<string, bool> @return)
+        public static ITest_Get_M1_MockCall Get(this global::TUnit.Mocks.Mock<global::ITest> mock, global::System.Func<int, bool>? @class, global::System.Func<string, bool>? @return)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_class = @class;
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_return = @return;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_class = @class is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)@class;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_return = @return is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)@return;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_class.Matcher, __fa_return.Matcher };
             return new ITest_Get_M1_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Get", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Mixed_Members.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Mixed_Members.verified.txt
index c7eee023cc..c3c12c7b51 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Mixed_Members.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Mixed_Members.verified.txt
@@ -182,9 +182,9 @@ namespace TUnit.Mocks.Generated
             return new IService_GetAsync_M3_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "GetAsync", matchers);
         }
 
-        public static IService_GetAsync_M3_MockCall GetAsync(this global::TUnit.Mocks.Mock<global::IService> mock, global::System.Func<int, bool> id)
+        public static IService_GetAsync_M3_MockCall GetAsync(this global::TUnit.Mocks.Mock<global::IService> mock, global::System.Func<int, bool>? id)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_id = id;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_id = id is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)id;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_id.Matcher };
             return new IService_GetAsync_M3_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "GetAsync", matchers);
         }
@@ -195,9 +195,9 @@ namespace TUnit.Mocks.Generated
             return new IService_Process_M4_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 4, "Process", matchers);
         }
 
-        public static IService_Process_M4_MockCall Process(this global::TUnit.Mocks.Mock<global::IService> mock, global::System.Func<string, bool> data)
+        public static IService_Process_M4_MockCall Process(this global::TUnit.Mocks.Mock<global::IService> mock, global::System.Func<string, bool>? data)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_data = data;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_data = data is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)data;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_data.Matcher };
             return new IService_Process_M4_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 4, "Process", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_NonSpan_RefStruct_Out_Ref_Parameters.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_NonSpan_RefStruct_Out_Ref_Parameters.verified.txt
index 3460bd045e..daa7c217d2 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_NonSpan_RefStruct_Out_Ref_Parameters.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_NonSpan_RefStruct_Out_Ref_Parameters.verified.txt
@@ -120,9 +120,9 @@ namespace TUnit.Mocks.Generated
             return new Sandbox_ICursorParser_TryRead_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "TryRead", matchers);
         }
 
-        public static Sandbox_ICursorParser_TryRead_M0_MockCall TryRead(this global::TUnit.Mocks.Mock<global::Sandbox.ICursorParser> mock, global::System.Func<string, bool> input)
+        public static Sandbox_ICursorParser_TryRead_M0_MockCall TryRead(this global::TUnit.Mocks.Mock<global::Sandbox.ICursorParser> mock, global::System.Func<string, bool>? input)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_input = input;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_input = input is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)input;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_input.Matcher };
             return new Sandbox_ICursorParser_TryRead_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "TryRead", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Nullable_Reference_Type_Parameters.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Nullable_Reference_Type_Parameters.verified.txt
index 063d6e0dfd..d3a4870704 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Nullable_Reference_Type_Parameters.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Nullable_Reference_Type_Parameters.verified.txt
@@ -135,9 +135,9 @@ namespace TUnit.Mocks.Generated
             return new IFoo_Bar_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Bar", matchers);
         }
 
-        public static IFoo_Bar_M0_MockCall Bar(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::System.Func<object?, bool> baz)
+        public static IFoo_Bar_M0_MockCall Bar(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::System.Func<object?, bool>? baz)
         {
-            global::TUnit.Mocks.Arguments.Arg<object?> __fa_baz = baz;
+            global::TUnit.Mocks.Arguments.Arg<object?> __fa_baz = baz is null ? global::TUnit.Mocks.Arguments.Arg.Is<object?>(default(object?)!) : (global::TUnit.Mocks.Arguments.Arg<object?>)baz;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_baz.Matcher };
             return new IFoo_Bar_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Bar", matchers);
         }
@@ -148,24 +148,24 @@ namespace TUnit.Mocks.Generated
             return new IFoo_GetValue_M1_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "GetValue", matchers);
         }
 
-        public static IFoo_GetValue_M1_MockCall GetValue(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::System.Func<string?, bool> key, global::TUnit.Mocks.Arguments.Arg<int> count)
+        public static IFoo_GetValue_M1_MockCall GetValue(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::System.Func<string?, bool>? key, global::TUnit.Mocks.Arguments.Arg<int> count)
         {
-            global::TUnit.Mocks.Arguments.Arg<string?> __fa_key = key;
+            global::TUnit.Mocks.Arguments.Arg<string?> __fa_key = key is null ? global::TUnit.Mocks.Arguments.Arg.Is<string?>(default(string?)!) : (global::TUnit.Mocks.Arguments.Arg<string?>)key;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_key.Matcher, count.Matcher };
             return new IFoo_GetValue_M1_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "GetValue", matchers);
         }
 
-        public static IFoo_GetValue_M1_MockCall GetValue(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::TUnit.Mocks.Arguments.Arg<string?> key, global::System.Func<int, bool> count)
+        public static IFoo_GetValue_M1_MockCall GetValue(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::TUnit.Mocks.Arguments.Arg<string?> key, global::System.Func<int, bool>? count)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_count = count;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_count = count is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)count;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { key.Matcher, __fa_count.Matcher };
             return new IFoo_GetValue_M1_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "GetValue", matchers);
         }
 
-        public static IFoo_GetValue_M1_MockCall GetValue(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::System.Func<string?, bool> key, global::System.Func<int, bool> count)
+        public static IFoo_GetValue_M1_MockCall GetValue(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::System.Func<string?, bool>? key, global::System.Func<int, bool>? count)
         {
-            global::TUnit.Mocks.Arguments.Arg<string?> __fa_key = key;
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_count = count;
+            global::TUnit.Mocks.Arguments.Arg<string?> __fa_key = key is null ? global::TUnit.Mocks.Arguments.Arg.Is<string?>(default(string?)!) : (global::TUnit.Mocks.Arguments.Arg<string?>)key;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_count = count is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)count;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_key.Matcher, __fa_count.Matcher };
             return new IFoo_GetValue_M1_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "GetValue", matchers);
         }
@@ -183,56 +183,56 @@ namespace TUnit.Mocks.Generated
             return new IFoo_Process_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Process", matchers);
         }
 
-        public static IFoo_Process_M2_MockCall Process(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::System.Func<string, bool> nonNull, global::TUnit.Mocks.Arguments.Arg<string?> nullable, global::TUnit.Mocks.Arguments.Arg<object?> obj)
+        public static IFoo_Process_M2_MockCall Process(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::System.Func<string, bool>? nonNull, global::TUnit.Mocks.Arguments.Arg<string?> nullable, global::TUnit.Mocks.Arguments.Arg<object?> obj)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_nonNull = nonNull;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_nonNull = nonNull is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)nonNull;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_nonNull.Matcher, nullable.Matcher, obj.Matcher };
             return new IFoo_Process_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Process", matchers);
         }
 
-        public static IFoo_Process_M2_MockCall Process(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::TUnit.Mocks.Arguments.Arg<string> nonNull, global::System.Func<string?, bool> nullable, global::TUnit.Mocks.Arguments.Arg<object?> obj)
+        public static IFoo_Process_M2_MockCall Process(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::TUnit.Mocks.Arguments.Arg<string> nonNull, global::System.Func<string?, bool>? nullable, global::TUnit.Mocks.Arguments.Arg<object?> obj)
         {
-            global::TUnit.Mocks.Arguments.Arg<string?> __fa_nullable = nullable;
+            global::TUnit.Mocks.Arguments.Arg<string?> __fa_nullable = nullable is null ? global::TUnit.Mocks.Arguments.Arg.Is<string?>(default(string?)!) : (global::TUnit.Mocks.Arguments.Arg<string?>)nullable;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { nonNull.Matcher, __fa_nullable.Matcher, obj.Matcher };
             return new IFoo_Process_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Process", matchers);
         }
 
-        public static IFoo_Process_M2_MockCall Process(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::System.Func<string, bool> nonNull, global::System.Func<string?, bool> nullable, global::TUnit.Mocks.Arguments.Arg<object?> obj)
+        public static IFoo_Process_M2_MockCall Process(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::System.Func<string, bool>? nonNull, global::System.Func<string?, bool>? nullable, global::TUnit.Mocks.Arguments.Arg<object?> obj)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_nonNull = nonNull;
-            global::TUnit.Mocks.Arguments.Arg<string?> __fa_nullable = nullable;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_nonNull = nonNull is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)nonNull;
+            global::TUnit.Mocks.Arguments.Arg<string?> __fa_nullable = nullable is null ? global::TUnit.Mocks.Arguments.Arg.Is<string?>(default(string?)!) : (global::TUnit.Mocks.Arguments.Arg<string?>)nullable;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_nonNull.Matcher, __fa_nullable.Matcher, obj.Matcher };
             return new IFoo_Process_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Process", matchers);
         }
 
-        public static IFoo_Process_M2_MockCall Process(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::TUnit.Mocks.Arguments.Arg<string> nonNull, global::TUnit.Mocks.Arguments.Arg<string?> nullable, global::System.Func<object?, bool> obj)
+        public static IFoo_Process_M2_MockCall Process(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::TUnit.Mocks.Arguments.Arg<string> nonNull, global::TUnit.Mocks.Arguments.Arg<string?> nullable, global::System.Func<object?, bool>? obj)
         {
-            global::TUnit.Mocks.Arguments.Arg<object?> __fa_obj = obj;
+            global::TUnit.Mocks.Arguments.Arg<object?> __fa_obj = obj is null ? global::TUnit.Mocks.Arguments.Arg.Is<object?>(default(object?)!) : (global::TUnit.Mocks.Arguments.Arg<object?>)obj;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { nonNull.Matcher, nullable.Matcher, __fa_obj.Matcher };
             return new IFoo_Process_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Process", matchers);
         }
 
-        public static IFoo_Process_M2_MockCall Process(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::System.Func<string, bool> nonNull, global::TUnit.Mocks.Arguments.Arg<string?> nullable, global::System.Func<object?, bool> obj)
+        public static IFoo_Process_M2_MockCall Process(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::System.Func<string, bool>? nonNull, global::TUnit.Mocks.Arguments.Arg<string?> nullable, global::System.Func<object?, bool>? obj)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_nonNull = nonNull;
-            global::TUnit.Mocks.Arguments.Arg<object?> __fa_obj = obj;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_nonNull = nonNull is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)nonNull;
+            global::TUnit.Mocks.Arguments.Arg<object?> __fa_obj = obj is null ? global::TUnit.Mocks.Arguments.Arg.Is<object?>(default(object?)!) : (global::TUnit.Mocks.Arguments.Arg<object?>)obj;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_nonNull.Matcher, nullable.Matcher, __fa_obj.Matcher };
             return new IFoo_Process_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Process", matchers);
         }
 
-        public static IFoo_Process_M2_MockCall Process(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::TUnit.Mocks.Arguments.Arg<string> nonNull, global::System.Func<string?, bool> nullable, global::System.Func<object?, bool> obj)
+        public static IFoo_Process_M2_MockCall Process(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::TUnit.Mocks.Arguments.Arg<string> nonNull, global::System.Func<string?, bool>? nullable, global::System.Func<object?, bool>? obj)
         {
-            global::TUnit.Mocks.Arguments.Arg<string?> __fa_nullable = nullable;
-            global::TUnit.Mocks.Arguments.Arg<object?> __fa_obj = obj;
+            global::TUnit.Mocks.Arguments.Arg<string?> __fa_nullable = nullable is null ? global::TUnit.Mocks.Arguments.Arg.Is<string?>(default(string?)!) : (global::TUnit.Mocks.Arguments.Arg<string?>)nullable;
+            global::TUnit.Mocks.Arguments.Arg<object?> __fa_obj = obj is null ? global::TUnit.Mocks.Arguments.Arg.Is<object?>(default(object?)!) : (global::TUnit.Mocks.Arguments.Arg<object?>)obj;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { nonNull.Matcher, __fa_nullable.Matcher, __fa_obj.Matcher };
             return new IFoo_Process_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Process", matchers);
         }
 
-        public static IFoo_Process_M2_MockCall Process(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::System.Func<string, bool> nonNull, global::System.Func<string?, bool> nullable, global::System.Func<object?, bool> obj)
+        public static IFoo_Process_M2_MockCall Process(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::System.Func<string, bool>? nonNull, global::System.Func<string?, bool>? nullable, global::System.Func<object?, bool>? obj)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_nonNull = nonNull;
-            global::TUnit.Mocks.Arguments.Arg<string?> __fa_nullable = nullable;
-            global::TUnit.Mocks.Arguments.Arg<object?> __fa_obj = obj;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_nonNull = nonNull is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)nonNull;
+            global::TUnit.Mocks.Arguments.Arg<string?> __fa_nullable = nullable is null ? global::TUnit.Mocks.Arguments.Arg.Is<string?>(default(string?)!) : (global::TUnit.Mocks.Arguments.Arg<string?>)nullable;
+            global::TUnit.Mocks.Arguments.Arg<object?> __fa_obj = obj is null ? global::TUnit.Mocks.Arguments.Arg.Is<object?>(default(object?)!) : (global::TUnit.Mocks.Arguments.Arg<object?>)obj;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_nonNull.Matcher, __fa_nullable.Matcher, __fa_obj.Matcher };
             return new IFoo_Process_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Process", matchers);
         }
@@ -250,9 +250,9 @@ namespace TUnit.Mocks.Generated
             return new IFoo_GetAsync_M3_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "GetAsync", matchers);
         }
 
-        public static IFoo_GetAsync_M3_MockCall GetAsync(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::System.Func<string?, bool> key)
+        public static IFoo_GetAsync_M3_MockCall GetAsync(this global::TUnit.Mocks.Mock<global::IFoo> mock, global::System.Func<string?, bool>? key)
         {
-            global::TUnit.Mocks.Arguments.Arg<string?> __fa_key = key;
+            global::TUnit.Mocks.Arguments.Arg<string?> __fa_key = key is null ? global::TUnit.Mocks.Arguments.Arg.Is<string?>(default(string?)!) : (global::TUnit.Mocks.Arguments.Arg<string?>)key;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_key.Matcher };
             return new IFoo_GetAsync_M3_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "GetAsync", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Obsolete_Members.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Obsolete_Members.verified.txt
index 89f14ada45..16155bb1ba 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Obsolete_Members.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Obsolete_Members.verified.txt
@@ -81,9 +81,9 @@ namespace TUnit.Mocks.Generated
             return new BaseDialog_Compute_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Compute", matchers);
         }
 
-        public static BaseDialog_Compute_M0_MockCall Compute(this global::TUnit.Mocks.Mock<global::BaseDialog> mock, global::System.Func<string?, bool> input)
+        public static BaseDialog_Compute_M0_MockCall Compute(this global::TUnit.Mocks.Mock<global::BaseDialog> mock, global::System.Func<string?, bool>? input)
         {
-            global::TUnit.Mocks.Arguments.Arg<string?> __fa_input = input;
+            global::TUnit.Mocks.Arguments.Arg<string?> __fa_input = input is null ? global::TUnit.Mocks.Arguments.Arg.Is<string?>(default(string?)!) : (global::TUnit.Mocks.Arguments.Arg<string?>)input;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_input.Matcher };
             return new BaseDialog_Compute_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Compute", matchers);
         }
@@ -409,24 +409,24 @@ namespace TUnit.Mocks.Generated
             return new IDialogService_Show_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Show", matchers);
         }
 
-        public static IDialogService_Show_M0_MockCall Show(this global::TUnit.Mocks.Mock<global::IDialogService> mock, global::System.Func<string?, bool> title, global::TUnit.Mocks.Arguments.Arg<string?> message)
+        public static IDialogService_Show_M0_MockCall Show(this global::TUnit.Mocks.Mock<global::IDialogService> mock, global::System.Func<string?, bool>? title, global::TUnit.Mocks.Arguments.Arg<string?> message)
         {
-            global::TUnit.Mocks.Arguments.Arg<string?> __fa_title = title;
+            global::TUnit.Mocks.Arguments.Arg<string?> __fa_title = title is null ? global::TUnit.Mocks.Arguments.Arg.Is<string?>(default(string?)!) : (global::TUnit.Mocks.Arguments.Arg<string?>)title;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_title.Matcher, message.Matcher };
             return new IDialogService_Show_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Show", matchers);
         }
 
-        public static IDialogService_Show_M0_MockCall Show(this global::TUnit.Mocks.Mock<global::IDialogService> mock, global::TUnit.Mocks.Arguments.Arg<string?> title, global::System.Func<string?, bool> message)
+        public static IDialogService_Show_M0_MockCall Show(this global::TUnit.Mocks.Mock<global::IDialogService> mock, global::TUnit.Mocks.Arguments.Arg<string?> title, global::System.Func<string?, bool>? message)
         {
-            global::TUnit.Mocks.Arguments.Arg<string?> __fa_message = message;
+            global::TUnit.Mocks.Arguments.Arg<string?> __fa_message = message is null ? global::TUnit.Mocks.Arguments.Arg.Is<string?>(default(string?)!) : (global::TUnit.Mocks.Arguments.Arg<string?>)message;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { title.Matcher, __fa_message.Matcher };
             return new IDialogService_Show_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Show", matchers);
         }
 
-        public static IDialogService_Show_M0_MockCall Show(this global::TUnit.Mocks.Mock<global::IDialogService> mock, global::System.Func<string?, bool> title, global::System.Func<string?, bool> message)
+        public static IDialogService_Show_M0_MockCall Show(this global::TUnit.Mocks.Mock<global::IDialogService> mock, global::System.Func<string?, bool>? title, global::System.Func<string?, bool>? message)
         {
-            global::TUnit.Mocks.Arguments.Arg<string?> __fa_title = title;
-            global::TUnit.Mocks.Arguments.Arg<string?> __fa_message = message;
+            global::TUnit.Mocks.Arguments.Arg<string?> __fa_title = title is null ? global::TUnit.Mocks.Arguments.Arg.Is<string?>(default(string?)!) : (global::TUnit.Mocks.Arguments.Arg<string?>)title;
+            global::TUnit.Mocks.Arguments.Arg<string?> __fa_message = message is null ? global::TUnit.Mocks.Arguments.Arg.Is<string?>(default(string?)!) : (global::TUnit.Mocks.Arguments.Arg<string?>)message;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_title.Matcher, __fa_message.Matcher };
             return new IDialogService_Show_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Show", matchers);
         }
@@ -444,9 +444,9 @@ namespace TUnit.Mocks.Generated
             return new IDialogService_ShowPanel_M1_MockCall<TData>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "ShowPanel", matchers, global::TUnit.Mocks.TypeArguments.Of<TData>.Value);
         }
 
-        public static IDialogService_ShowPanel_M1_MockCall<TData> ShowPanel<TData>(this global::TUnit.Mocks.Mock<global::IDialogService> mock, global::System.Func<TData?, bool> data) where TData : class
+        public static IDialogService_ShowPanel_M1_MockCall<TData> ShowPanel<TData>(this global::TUnit.Mocks.Mock<global::IDialogService> mock, global::System.Func<TData?, bool>? data) where TData : class
         {
-            global::TUnit.Mocks.Arguments.Arg<TData?> __fa_data = data;
+            global::TUnit.Mocks.Arguments.Arg<TData?> __fa_data = data is null ? global::TUnit.Mocks.Arguments.Arg.Is<TData?>(default(TData?)!) : (global::TUnit.Mocks.Arguments.Arg<TData?>)data;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_data.Matcher };
             return new IDialogService_ShowPanel_M1_MockCall<TData>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "ShowPanel", matchers, global::TUnit.Mocks.TypeArguments.Of<TData>.Value);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Out_Ref_Parameters.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Out_Ref_Parameters.verified.txt
index afe14f7d5f..d005bc9101 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Out_Ref_Parameters.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Out_Ref_Parameters.verified.txt
@@ -110,9 +110,9 @@ namespace TUnit.Mocks.Generated
             return new IDictionary_TryGetValue_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "TryGetValue", matchers);
         }
 
-        public static IDictionary_TryGetValue_M0_MockCall TryGetValue(this global::TUnit.Mocks.Mock<global::IDictionary> mock, global::System.Func<string, bool> key)
+        public static IDictionary_TryGetValue_M0_MockCall TryGetValue(this global::TUnit.Mocks.Mock<global::IDictionary> mock, global::System.Func<string, bool>? key)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_key = key;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_key = key is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)key;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_key.Matcher };
             return new IDictionary_TryGetValue_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "TryGetValue", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Overloaded_Methods.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Overloaded_Methods.verified.txt
index 4d530428b5..8924c3c446 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Overloaded_Methods.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Overloaded_Methods.verified.txt
@@ -108,9 +108,9 @@ namespace TUnit.Mocks.Generated
             return new IFormatter_Format_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Format", matchers);
         }
 
-        public static IFormatter_Format_M0_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::System.Func<string, bool> value)
+        public static IFormatter_Format_M0_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::System.Func<string, bool>? value)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_value = value;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)value;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_value.Matcher };
             return new IFormatter_Format_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Format", matchers);
         }
@@ -121,9 +121,9 @@ namespace TUnit.Mocks.Generated
             return new IFormatter_Format_M1_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Format", matchers);
         }
 
-        public static IFormatter_Format_M1_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::System.Func<int, bool> value)
+        public static IFormatter_Format_M1_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::System.Func<int, bool>? value)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_value = value;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)value;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_value.Matcher };
             return new IFormatter_Format_M1_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Format", matchers);
         }
@@ -134,24 +134,24 @@ namespace TUnit.Mocks.Generated
             return new IFormatter_Format_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Format", matchers);
         }
 
-        public static IFormatter_Format_M2_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::System.Func<string, bool> template, global::TUnit.Mocks.Arguments.Arg<string> arg1)
+        public static IFormatter_Format_M2_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::System.Func<string, bool>? template, global::TUnit.Mocks.Arguments.Arg<string> arg1)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_template = template;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_template = template is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)template;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_template.Matcher, arg1.Matcher };
             return new IFormatter_Format_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Format", matchers);
         }
 
-        public static IFormatter_Format_M2_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::TUnit.Mocks.Arguments.Arg<string> template, global::System.Func<string, bool> arg1)
+        public static IFormatter_Format_M2_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::TUnit.Mocks.Arguments.Arg<string> template, global::System.Func<string, bool>? arg1)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg1 = arg1;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg1 = arg1 is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)arg1;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { template.Matcher, __fa_arg1.Matcher };
             return new IFormatter_Format_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Format", matchers);
         }
 
-        public static IFormatter_Format_M2_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::System.Func<string, bool> template, global::System.Func<string, bool> arg1)
+        public static IFormatter_Format_M2_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::System.Func<string, bool>? template, global::System.Func<string, bool>? arg1)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_template = template;
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg1 = arg1;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_template = template is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)template;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg1 = arg1 is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)arg1;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_template.Matcher, __fa_arg1.Matcher };
             return new IFormatter_Format_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Format", matchers);
         }
@@ -162,56 +162,56 @@ namespace TUnit.Mocks.Generated
             return new IFormatter_Format_M3_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "Format", matchers);
         }
 
-        public static IFormatter_Format_M3_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::System.Func<string, bool> template, global::TUnit.Mocks.Arguments.Arg<string> arg1, global::TUnit.Mocks.Arguments.Arg<string> arg2)
+        public static IFormatter_Format_M3_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::System.Func<string, bool>? template, global::TUnit.Mocks.Arguments.Arg<string> arg1, global::TUnit.Mocks.Arguments.Arg<string> arg2)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_template = template;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_template = template is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)template;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_template.Matcher, arg1.Matcher, arg2.Matcher };
             return new IFormatter_Format_M3_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "Format", matchers);
         }
 
-        public static IFormatter_Format_M3_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::TUnit.Mocks.Arguments.Arg<string> template, global::System.Func<string, bool> arg1, global::TUnit.Mocks.Arguments.Arg<string> arg2)
+        public static IFormatter_Format_M3_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::TUnit.Mocks.Arguments.Arg<string> template, global::System.Func<string, bool>? arg1, global::TUnit.Mocks.Arguments.Arg<string> arg2)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg1 = arg1;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg1 = arg1 is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)arg1;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { template.Matcher, __fa_arg1.Matcher, arg2.Matcher };
             return new IFormatter_Format_M3_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "Format", matchers);
         }
 
-        public static IFormatter_Format_M3_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::System.Func<string, bool> template, global::System.Func<string, bool> arg1, global::TUnit.Mocks.Arguments.Arg<string> arg2)
+        public static IFormatter_Format_M3_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::System.Func<string, bool>? template, global::System.Func<string, bool>? arg1, global::TUnit.Mocks.Arguments.Arg<string> arg2)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_template = template;
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg1 = arg1;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_template = template is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)template;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg1 = arg1 is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)arg1;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_template.Matcher, __fa_arg1.Matcher, arg2.Matcher };
             return new IFormatter_Format_M3_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "Format", matchers);
         }
 
-        public static IFormatter_Format_M3_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::TUnit.Mocks.Arguments.Arg<string> template, global::TUnit.Mocks.Arguments.Arg<string> arg1, global::System.Func<string, bool> arg2)
+        public static IFormatter_Format_M3_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::TUnit.Mocks.Arguments.Arg<string> template, global::TUnit.Mocks.Arguments.Arg<string> arg1, global::System.Func<string, bool>? arg2)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg2 = arg2;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg2 = arg2 is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)arg2;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { template.Matcher, arg1.Matcher, __fa_arg2.Matcher };
             return new IFormatter_Format_M3_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "Format", matchers);
         }
 
-        public static IFormatter_Format_M3_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::System.Func<string, bool> template, global::TUnit.Mocks.Arguments.Arg<string> arg1, global::System.Func<string, bool> arg2)
+        public static IFormatter_Format_M3_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::System.Func<string, bool>? template, global::TUnit.Mocks.Arguments.Arg<string> arg1, global::System.Func<string, bool>? arg2)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_template = template;
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg2 = arg2;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_template = template is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)template;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg2 = arg2 is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)arg2;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_template.Matcher, arg1.Matcher, __fa_arg2.Matcher };
             return new IFormatter_Format_M3_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "Format", matchers);
         }
 
-        public static IFormatter_Format_M3_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::TUnit.Mocks.Arguments.Arg<string> template, global::System.Func<string, bool> arg1, global::System.Func<string, bool> arg2)
+        public static IFormatter_Format_M3_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::TUnit.Mocks.Arguments.Arg<string> template, global::System.Func<string, bool>? arg1, global::System.Func<string, bool>? arg2)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg1 = arg1;
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg2 = arg2;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg1 = arg1 is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)arg1;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg2 = arg2 is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)arg2;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { template.Matcher, __fa_arg1.Matcher, __fa_arg2.Matcher };
             return new IFormatter_Format_M3_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "Format", matchers);
         }
 
-        public static IFormatter_Format_M3_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::System.Func<string, bool> template, global::System.Func<string, bool> arg1, global::System.Func<string, bool> arg2)
+        public static IFormatter_Format_M3_MockCall Format(this global::TUnit.Mocks.Mock<global::IFormatter> mock, global::System.Func<string, bool>? template, global::System.Func<string, bool>? arg1, global::System.Func<string, bool>? arg2)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_template = template;
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg1 = arg1;
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg2 = arg2;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_template = template is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)template;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg1 = arg1 is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)arg1;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_arg2 = arg2 is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)arg2;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_template.Matcher, __fa_arg1.Matcher, __fa_arg2.Matcher };
             return new IFormatter_Format_M3_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "Format", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Params_Array_Parameter.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Params_Array_Parameter.verified.txt
index dd3302483d..fcaf00629e 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Params_Array_Parameter.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Params_Array_Parameter.verified.txt
@@ -108,9 +108,9 @@ namespace TUnit.Mocks.Generated
             return new IParamsSink_Sum_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Sum", matchers);
         }
 
-        public static IParamsSink_Sum_M0_MockCall Sum(this global::TUnit.Mocks.Mock<global::IParamsSink> mock, global::System.Func<int[], bool> values)
+        public static IParamsSink_Sum_M0_MockCall Sum(this global::TUnit.Mocks.Mock<global::IParamsSink> mock, global::System.Func<int[], bool>? values)
         {
-            global::TUnit.Mocks.Arguments.Arg<int[]> __fa_values = values;
+            global::TUnit.Mocks.Arguments.Arg<int[]> __fa_values = values is null ? global::TUnit.Mocks.Arguments.Arg.Is<int[]>(default(int[])!) : (global::TUnit.Mocks.Arguments.Arg<int[]>)values;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_values.Matcher };
             return new IParamsSink_Sum_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Sum", matchers);
         }
@@ -138,9 +138,9 @@ namespace TUnit.Mocks.Generated
             return new IParamsSink_Render_M1_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Render", matchers);
         }
 
-        public static IParamsSink_Render_M1_MockCall Render(this global::TUnit.Mocks.Mock<global::IParamsSink> mock, global::System.Func<object[], bool> args)
+        public static IParamsSink_Render_M1_MockCall Render(this global::TUnit.Mocks.Mock<global::IParamsSink> mock, global::System.Func<object[], bool>? args)
         {
-            global::TUnit.Mocks.Arguments.Arg<object[]> __fa_args = args;
+            global::TUnit.Mocks.Arguments.Arg<object[]> __fa_args = args is null ? global::TUnit.Mocks.Arguments.Arg.Is<object[]>(default(object[])!) : (global::TUnit.Mocks.Arguments.Arg<object[]>)args;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_args.Matcher };
             return new IParamsSink_Render_M1_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Render", matchers);
         }
@@ -168,24 +168,24 @@ namespace TUnit.Mocks.Generated
             return new IParamsSink_Combine_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Combine", matchers);
         }
 
-        public static IParamsSink_Combine_M2_MockCall Combine(this global::TUnit.Mocks.Mock<global::IParamsSink> mock, global::System.Func<string, bool> prefix, global::TUnit.Mocks.Arguments.Arg<string[]> parts)
+        public static IParamsSink_Combine_M2_MockCall Combine(this global::TUnit.Mocks.Mock<global::IParamsSink> mock, global::System.Func<string, bool>? prefix, global::TUnit.Mocks.Arguments.Arg<string[]> parts)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_prefix = prefix;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_prefix = prefix is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)prefix;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_prefix.Matcher, parts.Matcher };
             return new IParamsSink_Combine_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Combine", matchers);
         }
 
-        public static IParamsSink_Combine_M2_MockCall Combine(this global::TUnit.Mocks.Mock<global::IParamsSink> mock, global::TUnit.Mocks.Arguments.Arg<string> prefix, global::System.Func<string[], bool> parts)
+        public static IParamsSink_Combine_M2_MockCall Combine(this global::TUnit.Mocks.Mock<global::IParamsSink> mock, global::TUnit.Mocks.Arguments.Arg<string> prefix, global::System.Func<string[], bool>? parts)
         {
-            global::TUnit.Mocks.Arguments.Arg<string[]> __fa_parts = parts;
+            global::TUnit.Mocks.Arguments.Arg<string[]> __fa_parts = parts is null ? global::TUnit.Mocks.Arguments.Arg.Is<string[]>(default(string[])!) : (global::TUnit.Mocks.Arguments.Arg<string[]>)parts;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { prefix.Matcher, __fa_parts.Matcher };
             return new IParamsSink_Combine_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Combine", matchers);
         }
 
-        public static IParamsSink_Combine_M2_MockCall Combine(this global::TUnit.Mocks.Mock<global::IParamsSink> mock, global::System.Func<string, bool> prefix, global::System.Func<string[], bool> parts)
+        public static IParamsSink_Combine_M2_MockCall Combine(this global::TUnit.Mocks.Mock<global::IParamsSink> mock, global::System.Func<string, bool>? prefix, global::System.Func<string[], bool>? parts)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_prefix = prefix;
-            global::TUnit.Mocks.Arguments.Arg<string[]> __fa_parts = parts;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_prefix = prefix is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)prefix;
+            global::TUnit.Mocks.Arguments.Arg<string[]> __fa_parts = parts is null ? global::TUnit.Mocks.Arguments.Arg.Is<string[]>(default(string[])!) : (global::TUnit.Mocks.Arguments.Arg<string[]>)parts;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_prefix.Matcher, __fa_parts.Matcher };
             return new IParamsSink_Combine_M2_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Combine", matchers);
         }
@@ -220,9 +220,9 @@ namespace TUnit.Mocks.Generated
             return new IParamsSink_First_M3_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "First", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
 
-        public static IParamsSink_First_M3_MockCall<T> First<T>(this global::TUnit.Mocks.Mock<global::IParamsSink> mock, global::System.Func<T[], bool> items)
+        public static IParamsSink_First_M3_MockCall<T> First<T>(this global::TUnit.Mocks.Mock<global::IParamsSink> mock, global::System.Func<T[], bool>? items)
         {
-            global::TUnit.Mocks.Arguments.Arg<T[]> __fa_items = items;
+            global::TUnit.Mocks.Arguments.Arg<T[]> __fa_items = items is null ? global::TUnit.Mocks.Arguments.Arg.Is<T[]>(default(T[])!) : (global::TUnit.Mocks.Arguments.Arg<T[]>)items;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_items.Matcher };
             return new IParamsSink_First_M3_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 3, "First", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Static_Abstract_Transitive_Return_Type.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Static_Abstract_Transitive_Return_Type.verified.txt
index e823569b68..9aa76353b9 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Static_Abstract_Transitive_Return_Type.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Static_Abstract_Transitive_Return_Type.verified.txt
@@ -94,9 +94,9 @@ namespace TUnit.Mocks.Generated
             return new IMyService_GetValue_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "GetValue", matchers);
         }
 
-        public static IMyService_GetValue_M0_MockCall GetValue(this global::TUnit.Mocks.Mock<global::IMyService> mock, global::System.Func<string, bool> key)
+        public static IMyService_GetValue_M0_MockCall GetValue(this global::TUnit.Mocks.Mock<global::IMyService> mock, global::System.Func<string, bool>? key)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_key = key;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_key = key is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)key;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_key.Matcher };
             return new IMyService_GetValue_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "GetValue", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Type_Parameters_Named_Like_Numeric_Types.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Type_Parameters_Named_Like_Numeric_Types.verified.txt
index 48b548288a..7de3be5cc9 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Type_Parameters_Named_Like_Numeric_Types.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Type_Parameters_Named_Like_Numeric_Types.verified.txt
@@ -19,10 +19,10 @@ public sealed class INumericNamed_Int32_Mock<Int32> : global::TUnit.Mocks.Mock<g
         return new INumericNamed_Int32__RoundtripAsync_M1_MockCall<Int64, Int32>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "RoundtripAsync", matchers, global::TUnit.Mocks.TypeArguments.Of<Int64>.Value);
     }
 
-    public INumericNamed_Int32__RoundtripAsync_M1_MockCall<Int64, Int32> RoundtripAsync<Int64>(global::System.Func<Int64, bool> value)
+    public INumericNamed_Int32__RoundtripAsync_M1_MockCall<Int64, Int32> RoundtripAsync<Int64>(global::System.Func<Int64, bool>? value)
     {
         var mock = this;
-        global::TUnit.Mocks.Arguments.Arg<Int64> __fa_value = value;
+        global::TUnit.Mocks.Arguments.Arg<Int64> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<Int64>(default(Int64)!) : (global::TUnit.Mocks.Arguments.Arg<Int64>)value;
         var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_value.Matcher };
         return new INumericNamed_Int32__RoundtripAsync_M1_MockCall<Int64, Int32>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "RoundtripAsync", matchers, global::TUnit.Mocks.TypeArguments.Of<Int64>.Value);
     }
@@ -137,9 +137,9 @@ namespace TUnit.Mocks.Generated
                 return new INumericNamed_Int32__RoundtripAsync_M1_MockCall<Int64, Int32>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "RoundtripAsync", matchers, global::TUnit.Mocks.TypeArguments.Of<Int64>.Value);
             }
 
-            public INumericNamed_Int32__RoundtripAsync_M1_MockCall<Int64, Int32> RoundtripAsync<Int64>(global::System.Func<Int64, bool> value)
+            public INumericNamed_Int32__RoundtripAsync_M1_MockCall<Int64, Int32> RoundtripAsync<Int64>(global::System.Func<Int64, bool>? value)
             {
-                global::TUnit.Mocks.Arguments.Arg<Int64> __fa_value = value;
+                global::TUnit.Mocks.Arguments.Arg<Int64> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<Int64>(default(Int64)!) : (global::TUnit.Mocks.Arguments.Arg<Int64>)value;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_value.Matcher };
                 return new INumericNamed_Int32__RoundtripAsync_M1_MockCall<Int64, Int32>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "RoundtripAsync", matchers, global::TUnit.Mocks.TypeArguments.Of<Int64>.Value);
             }
@@ -152,9 +152,9 @@ namespace TUnit.Mocks.Generated
                 return new INumericNamed_Int32__RoundtripAsync_M1_MockCall<Int64, Int32>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "RoundtripAsync", matchers, global::TUnit.Mocks.TypeArguments.Of<Int64>.Value);
             }
 
-            public INumericNamed_Int32__RoundtripAsync_M1_MockCall<Int64, Int32> RoundtripAsync<Int64>(global::System.Func<Int64, bool> value)
+            public INumericNamed_Int32__RoundtripAsync_M1_MockCall<Int64, Int32> RoundtripAsync<Int64>(global::System.Func<Int64, bool>? value)
             {
-                global::TUnit.Mocks.Arguments.Arg<Int64> __fa_value = value;
+                global::TUnit.Mocks.Arguments.Arg<Int64> __fa_value = value is null ? global::TUnit.Mocks.Arguments.Arg.Is<Int64>(default(Int64)!) : (global::TUnit.Mocks.Arguments.Arg<Int64>)value;
                 var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_value.Matcher };
                 return new INumericNamed_Int32__RoundtripAsync_M1_MockCall<Int64, Int32>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "RoundtripAsync", matchers, global::TUnit.Mocks.TypeArguments.Of<Int64>.Value);
             }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Multi_Interface_Mock_With_Secondary_Setup_Surface.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Multi_Interface_Mock_With_Secondary_Setup_Surface.verified.txt
index db4dc2bcd1..aaf33e0de6 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Multi_Interface_Mock_With_Secondary_Setup_Surface.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Multi_Interface_Mock_With_Secondary_Setup_Surface.verified.txt
@@ -97,9 +97,9 @@ namespace TUnit.Mocks.Generated
             return new IMultiLogger_Log_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Log", matchers);
         }
 
-        public static IMultiLogger_Log_M0_MockCall Log(this global::TUnit.Mocks.Mock<global::IMultiLogger> mock, global::System.Func<string, bool> message)
+        public static IMultiLogger_Log_M0_MockCall Log(this global::TUnit.Mocks.Mock<global::IMultiLogger> mock, global::System.Func<string, bool>? message)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_message = message;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_message = message is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)message;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_message.Matcher };
             return new IMultiLogger_Log_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Log", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Multi_Method_Interface.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Multi_Method_Interface.verified.txt
index 977da7fbda..a2e8b21a3c 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Multi_Method_Interface.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Multi_Method_Interface.verified.txt
@@ -104,24 +104,24 @@ namespace TUnit.Mocks.Generated
             return new ICalculator_Add_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Add", matchers);
         }
 
-        public static ICalculator_Add_M0_MockCall Add(this global::TUnit.Mocks.Mock<global::ICalculator> mock, global::System.Func<int, bool> a, global::TUnit.Mocks.Arguments.Arg<int> b)
+        public static ICalculator_Add_M0_MockCall Add(this global::TUnit.Mocks.Mock<global::ICalculator> mock, global::System.Func<int, bool>? a, global::TUnit.Mocks.Arguments.Arg<int> b)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_a = a;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_a = a is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)a;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_a.Matcher, b.Matcher };
             return new ICalculator_Add_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Add", matchers);
         }
 
-        public static ICalculator_Add_M0_MockCall Add(this global::TUnit.Mocks.Mock<global::ICalculator> mock, global::TUnit.Mocks.Arguments.Arg<int> a, global::System.Func<int, bool> b)
+        public static ICalculator_Add_M0_MockCall Add(this global::TUnit.Mocks.Mock<global::ICalculator> mock, global::TUnit.Mocks.Arguments.Arg<int> a, global::System.Func<int, bool>? b)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_b = b;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_b = b is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)b;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { a.Matcher, __fa_b.Matcher };
             return new ICalculator_Add_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Add", matchers);
         }
 
-        public static ICalculator_Add_M0_MockCall Add(this global::TUnit.Mocks.Mock<global::ICalculator> mock, global::System.Func<int, bool> a, global::System.Func<int, bool> b)
+        public static ICalculator_Add_M0_MockCall Add(this global::TUnit.Mocks.Mock<global::ICalculator> mock, global::System.Func<int, bool>? a, global::System.Func<int, bool>? b)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_a = a;
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_b = b;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_a = a is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)a;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_b = b is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)b;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_a.Matcher, __fa_b.Matcher };
             return new ICalculator_Add_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Add", matchers);
         }
@@ -139,24 +139,24 @@ namespace TUnit.Mocks.Generated
             return new ICalculator_Subtract_M1_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Subtract", matchers);
         }
 
-        public static ICalculator_Subtract_M1_MockCall Subtract(this global::TUnit.Mocks.Mock<global::ICalculator> mock, global::System.Func<int, bool> a, global::TUnit.Mocks.Arguments.Arg<int> b)
+        public static ICalculator_Subtract_M1_MockCall Subtract(this global::TUnit.Mocks.Mock<global::ICalculator> mock, global::System.Func<int, bool>? a, global::TUnit.Mocks.Arguments.Arg<int> b)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_a = a;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_a = a is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)a;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_a.Matcher, b.Matcher };
             return new ICalculator_Subtract_M1_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Subtract", matchers);
         }
 
-        public static ICalculator_Subtract_M1_MockCall Subtract(this global::TUnit.Mocks.Mock<global::ICalculator> mock, global::TUnit.Mocks.Arguments.Arg<int> a, global::System.Func<int, bool> b)
+        public static ICalculator_Subtract_M1_MockCall Subtract(this global::TUnit.Mocks.Mock<global::ICalculator> mock, global::TUnit.Mocks.Arguments.Arg<int> a, global::System.Func<int, bool>? b)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_b = b;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_b = b is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)b;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { a.Matcher, __fa_b.Matcher };
             return new ICalculator_Subtract_M1_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Subtract", matchers);
         }
 
-        public static ICalculator_Subtract_M1_MockCall Subtract(this global::TUnit.Mocks.Mock<global::ICalculator> mock, global::System.Func<int, bool> a, global::System.Func<int, bool> b)
+        public static ICalculator_Subtract_M1_MockCall Subtract(this global::TUnit.Mocks.Mock<global::ICalculator> mock, global::System.Func<int, bool>? a, global::System.Func<int, bool>? b)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_a = a;
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_b = b;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_a = a is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)a;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_b = b is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)b;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_a.Matcher, __fa_b.Matcher };
             return new ICalculator_Subtract_M1_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Subtract", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_Filters_Internal_Virtual_Members_From_External_Assembly.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_Filters_Internal_Virtual_Members_From_External_Assembly.verified.txt
index bf4f27104c..10b860d5bd 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_Filters_Internal_Virtual_Members_From_External_Assembly.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_Filters_Internal_Virtual_Members_From_External_Assembly.verified.txt
@@ -111,9 +111,9 @@ namespace TUnit.Mocks.Generated
             return new ExternalLib_ExternalClient_PublicMethod_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "PublicMethod", matchers);
         }
 
-        public static ExternalLib_ExternalClient_PublicMethod_M0_MockCall PublicMethod(this global::TUnit.Mocks.Mock<global::ExternalLib.ExternalClient> mock, global::System.Func<string, bool> input)
+        public static ExternalLib_ExternalClient_PublicMethod_M0_MockCall PublicMethod(this global::TUnit.Mocks.Mock<global::ExternalLib.ExternalClient> mock, global::System.Func<string, bool>? input)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_input = input;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_input = input is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)input;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_input.Matcher };
             return new ExternalLib_ExternalClient_PublicMethod_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "PublicMethod", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_Filters_Members_With_Internal_Signature_Types.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_Filters_Members_With_Internal_Signature_Types.verified.txt
index 18bd74095f..6d7e8f5447 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_Filters_Members_With_Internal_Signature_Types.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_Filters_Members_With_Internal_Signature_Types.verified.txt
@@ -83,9 +83,9 @@ namespace TUnit.Mocks.Generated
             return new ExternalLib_ServiceClient_GetValue_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "GetValue", matchers);
         }
 
-        public static ExternalLib_ServiceClient_GetValue_M0_MockCall GetValue(this global::TUnit.Mocks.Mock<global::ExternalLib.ServiceClient> mock, global::System.Func<string, bool> key)
+        public static ExternalLib_ServiceClient_GetValue_M0_MockCall GetValue(this global::TUnit.Mocks.Mock<global::ExternalLib.ServiceClient> mock, global::System.Func<string, bool>? key)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_key = key;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_key = key is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)key;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_key.Matcher };
             return new ExternalLib_ServiceClient_GetValue_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "GetValue", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_With_Generic_Constrained_Virtual_Methods.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_With_Generic_Constrained_Virtual_Methods.verified.txt
index b1dfc95cbe..9dfe3b0f9a 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_With_Generic_Constrained_Virtual_Methods.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_With_Generic_Constrained_Virtual_Methods.verified.txt
@@ -103,9 +103,9 @@ namespace TUnit.Mocks.Generated
             return new BaseService_GetById_M0_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "GetById", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
 
-        public static BaseService_GetById_M0_MockCall<T> GetById<T>(this global::TUnit.Mocks.Mock<global::BaseService> mock, global::System.Func<int, bool> id) where T : class
+        public static BaseService_GetById_M0_MockCall<T> GetById<T>(this global::TUnit.Mocks.Mock<global::BaseService> mock, global::System.Func<int, bool>? id) where T : class
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_id = id;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_id = id is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)id;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_id.Matcher };
             return new BaseService_GetById_M0_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "GetById", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
@@ -116,9 +116,9 @@ namespace TUnit.Mocks.Generated
             return new BaseService_Save_M1_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Save", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
 
-        public static BaseService_Save_M1_MockCall<T> Save<T>(this global::TUnit.Mocks.Mock<global::BaseService> mock, global::System.Func<T, bool> entity) where T : class, new()
+        public static BaseService_Save_M1_MockCall<T> Save<T>(this global::TUnit.Mocks.Mock<global::BaseService> mock, global::System.Func<T, bool>? entity) where T : class, new()
         {
-            global::TUnit.Mocks.Arguments.Arg<T> __fa_entity = entity;
+            global::TUnit.Mocks.Arguments.Arg<T> __fa_entity = entity is null ? global::TUnit.Mocks.Arguments.Arg.Is<T>(default(T)!) : (global::TUnit.Mocks.Arguments.Arg<T>)entity;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_entity.Matcher };
             return new BaseService_Save_M1_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Save", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
@@ -129,9 +129,9 @@ namespace TUnit.Mocks.Generated
             return new BaseService_Transform_M2_MockCall<TInput, TResult>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Transform", matchers, global::TUnit.Mocks.TypeArguments.Of<TInput, TResult>.Value);
         }
 
-        public static BaseService_Transform_M2_MockCall<TInput, TResult> Transform<TInput, TResult>(this global::TUnit.Mocks.Mock<global::BaseService> mock, global::System.Func<TInput, bool> input) where TInput : notnull where TResult : struct
+        public static BaseService_Transform_M2_MockCall<TInput, TResult> Transform<TInput, TResult>(this global::TUnit.Mocks.Mock<global::BaseService> mock, global::System.Func<TInput, bool>? input) where TInput : notnull where TResult : struct
         {
-            global::TUnit.Mocks.Arguments.Arg<TInput> __fa_input = input;
+            global::TUnit.Mocks.Arguments.Arg<TInput> __fa_input = input is null ? global::TUnit.Mocks.Arguments.Arg.Is<TInput>(default(TInput)!) : (global::TUnit.Mocks.Arguments.Arg<TInput>)input;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_input.Matcher };
             return new BaseService_Transform_M2_MockCall<TInput, TResult>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 2, "Transform", matchers, global::TUnit.Mocks.TypeArguments.Of<TInput, TResult>.Value);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/SelfEquatable_Generates_EqualsOf_GetHashCodeOf_ToStringOf.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/SelfEquatable_Generates_EqualsOf_GetHashCodeOf_ToStringOf.verified.txt
index 1e5dd9af51..9ee9b15bef 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/SelfEquatable_Generates_EqualsOf_GetHashCodeOf_ToStringOf.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/SelfEquatable_Generates_EqualsOf_GetHashCodeOf_ToStringOf.verified.txt
@@ -117,9 +117,9 @@ namespace TUnit.Mocks.Generated
             return new SelfEquatableSnapshot_Equals_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Equals", matchers);
         }
 
-        public static SelfEquatableSnapshot_Equals_M0_MockCall EqualsOf(this global::TUnit.Mocks.Mock<global::SelfEquatableSnapshot> mock, global::System.Func<global::SelfEquatableSnapshot?, bool> other)
+        public static SelfEquatableSnapshot_Equals_M0_MockCall EqualsOf(this global::TUnit.Mocks.Mock<global::SelfEquatableSnapshot> mock, global::System.Func<global::SelfEquatableSnapshot?, bool>? other)
         {
-            global::TUnit.Mocks.Arguments.Arg<global::SelfEquatableSnapshot?> __fa_other = other;
+            global::TUnit.Mocks.Arguments.Arg<global::SelfEquatableSnapshot?> __fa_other = other is null ? global::TUnit.Mocks.Arguments.Arg.Is<global::SelfEquatableSnapshot?>(default(global::SelfEquatableSnapshot?)!) : (global::TUnit.Mocks.Arguments.Arg<global::SelfEquatableSnapshot?>)other;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_other.Matcher };
             return new SelfEquatableSnapshot_Equals_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Equals", matchers);
         }
@@ -130,9 +130,9 @@ namespace TUnit.Mocks.Generated
             return new SelfEquatableSnapshot_Equals_M1_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Equals", matchers);
         }
 
-        public static SelfEquatableSnapshot_Equals_M1_MockCall EqualsOf(this global::TUnit.Mocks.Mock<global::SelfEquatableSnapshot> mock, global::System.Func<object?, bool> obj)
+        public static SelfEquatableSnapshot_Equals_M1_MockCall EqualsOf(this global::TUnit.Mocks.Mock<global::SelfEquatableSnapshot> mock, global::System.Func<object?, bool>? obj)
         {
-            global::TUnit.Mocks.Arguments.Arg<object?> __fa_obj = obj;
+            global::TUnit.Mocks.Arguments.Arg<object?> __fa_obj = obj is null ? global::TUnit.Mocks.Arguments.Arg.Is<object?>(default(object?)!) : (global::TUnit.Mocks.Arguments.Arg<object?>)obj;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_obj.Matcher };
             return new SelfEquatableSnapshot_Equals_M1_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Equals", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Simple_Interface_With_One_Method.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Simple_Interface_With_One_Method.verified.txt
index f0ee1f4db4..dad436ee47 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Simple_Interface_With_One_Method.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Simple_Interface_With_One_Method.verified.txt
@@ -87,9 +87,9 @@ namespace TUnit.Mocks.Generated
             return new IGreeter_Greet_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Greet", matchers);
         }
 
-        public static IGreeter_Greet_M0_MockCall Greet(this global::TUnit.Mocks.Mock<global::IGreeter> mock, global::System.Func<string, bool> name)
+        public static IGreeter_Greet_M0_MockCall Greet(this global::TUnit.Mocks.Mock<global::IGreeter> mock, global::System.Func<string, bool>? name)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_name = name;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_name = name is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)name;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_name.Matcher };
             return new IGreeter_Greet_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Greet", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Static_Extension_Discovery_Without_Mock_Of.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Static_Extension_Discovery_Without_Mock_Of.verified.txt
index 891674a791..7d45efff68 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Static_Extension_Discovery_Without_Mock_Of.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Static_Extension_Discovery_Without_Mock_Of.verified.txt
@@ -97,9 +97,9 @@ namespace TUnit.Mocks.Generated
             return new INotifier_Notify_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Notify", matchers);
         }
 
-        public static INotifier_Notify_M0_MockCall Notify(this global::TUnit.Mocks.Mock<global::INotifier> mock, global::System.Func<string, bool> message)
+        public static INotifier_Notify_M0_MockCall Notify(this global::TUnit.Mocks.Mock<global::INotifier> mock, global::System.Func<string, bool>? message)
         {
-            global::TUnit.Mocks.Arguments.Arg<string> __fa_message = message;
+            global::TUnit.Mocks.Arguments.Arg<string> __fa_message = message is null ? global::TUnit.Mocks.Arguments.Arg.Is<string>(default(string)!) : (global::TUnit.Mocks.Arguments.Arg<string>)message;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_message.Matcher };
             return new INotifier_Notify_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Notify", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Type_Mocked_Regularly_And_Wrapped.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Type_Mocked_Regularly_And_Wrapped.verified.txt
index e2f808ec91..07bf75af8f 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Type_Mocked_Regularly_And_Wrapped.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Type_Mocked_Regularly_And_Wrapped.verified.txt
@@ -110,24 +110,24 @@ namespace TUnit.Mocks.Generated
             return new TestNamespace_Calculator_Add_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Add", matchers);
         }
 
-        public static TestNamespace_Calculator_Add_M0_MockCall Add(this global::TUnit.Mocks.Mock<global::TestNamespace.Calculator> mock, global::System.Func<int, bool> a, global::TUnit.Mocks.Arguments.Arg<int> b)
+        public static TestNamespace_Calculator_Add_M0_MockCall Add(this global::TUnit.Mocks.Mock<global::TestNamespace.Calculator> mock, global::System.Func<int, bool>? a, global::TUnit.Mocks.Arguments.Arg<int> b)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_a = a;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_a = a is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)a;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_a.Matcher, b.Matcher };
             return new TestNamespace_Calculator_Add_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Add", matchers);
         }
 
-        public static TestNamespace_Calculator_Add_M0_MockCall Add(this global::TUnit.Mocks.Mock<global::TestNamespace.Calculator> mock, global::TUnit.Mocks.Arguments.Arg<int> a, global::System.Func<int, bool> b)
+        public static TestNamespace_Calculator_Add_M0_MockCall Add(this global::TUnit.Mocks.Mock<global::TestNamespace.Calculator> mock, global::TUnit.Mocks.Arguments.Arg<int> a, global::System.Func<int, bool>? b)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_b = b;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_b = b is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)b;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { a.Matcher, __fa_b.Matcher };
             return new TestNamespace_Calculator_Add_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Add", matchers);
         }
 
-        public static TestNamespace_Calculator_Add_M0_MockCall Add(this global::TUnit.Mocks.Mock<global::TestNamespace.Calculator> mock, global::System.Func<int, bool> a, global::System.Func<int, bool> b)
+        public static TestNamespace_Calculator_Add_M0_MockCall Add(this global::TUnit.Mocks.Mock<global::TestNamespace.Calculator> mock, global::System.Func<int, bool>? a, global::System.Func<int, bool>? b)
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_a = a;
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_b = b;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_a = a is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)a;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_b = b is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)b;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_a.Matcher, __fa_b.Matcher };
             return new TestNamespace_Calculator_Add_M0_MockCall(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Add", matchers);
         }
diff --git a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Wrap_Mock_With_Generic_Constrained_Virtual_Methods.verified.txt b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Wrap_Mock_With_Generic_Constrained_Virtual_Methods.verified.txt
index e99d5a33ff..cd549cdcee 100644
--- a/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Wrap_Mock_With_Generic_Constrained_Virtual_Methods.verified.txt
+++ b/tests/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Wrap_Mock_With_Generic_Constrained_Virtual_Methods.verified.txt
@@ -12,9 +12,9 @@ namespace TUnit.Mocks.Generated
             return new Repository_Get_M0_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Get", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
 
-        public static Repository_Get_M0_MockCall<T> Get<T>(this global::TUnit.Mocks.Mock<global::Repository> mock, global::System.Func<int, bool> id) where T : class
+        public static Repository_Get_M0_MockCall<T> Get<T>(this global::TUnit.Mocks.Mock<global::Repository> mock, global::System.Func<int, bool>? id) where T : class
         {
-            global::TUnit.Mocks.Arguments.Arg<int> __fa_id = id;
+            global::TUnit.Mocks.Arguments.Arg<int> __fa_id = id is null ? global::TUnit.Mocks.Arguments.Arg.Is<int>(default(int)!) : (global::TUnit.Mocks.Arguments.Arg<int>)id;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_id.Matcher };
             return new Repository_Get_M0_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 0, "Get", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
@@ -25,9 +25,9 @@ namespace TUnit.Mocks.Generated
             return new Repository_Store_M1_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Store", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
 
-        public static Repository_Store_M1_MockCall<T> Store<T>(this global::TUnit.Mocks.Mock<global::Repository> mock, global::System.Func<T, bool> item) where T : class, new()
+        public static Repository_Store_M1_MockCall<T> Store<T>(this global::TUnit.Mocks.Mock<global::Repository> mock, global::System.Func<T, bool>? item) where T : class, new()
         {
-            global::TUnit.Mocks.Arguments.Arg<T> __fa_item = item;
+            global::TUnit.Mocks.Arguments.Arg<T> __fa_item = item is null ? global::TUnit.Mocks.Arguments.Arg.Is<T>(default(T)!) : (global::TUnit.Mocks.Arguments.Arg<T>)item;
             var matchers = new global::TUnit.Mocks.Arguments.IArgumentMatcher[] { __fa_item.Matcher };
             return new Repository_Store_M1_MockCall<T>(global::TUnit.Mocks.MockRegistry.GetEngine(mock), 1, "Store", matchers, global::TUnit.Mocks.TypeArguments.Of<T>.Value);
         }
diff --git a/tests/TUnit.Mocks.Tests/Issue5425Tests.cs b/tests/TUnit.Mocks.Tests/Issue5425Tests.cs
index 148cc5873b..c17c0999c3 100644
--- a/tests/TUnit.Mocks.Tests/Issue5425Tests.cs
+++ b/tests/TUnit.Mocks.Tests/Issue5425Tests.cs
@@ -1,6 +1,6 @@
 #nullable enable
 
-// The project file promotes the nullability warnings that #5424 / #5425 produced into errors so any
+// The project WarningsAsErrors setting promotes the nullability warnings that #5424 / #5425 produced into errors so any
 // regression in the source generator (where the generated mock loses nullability
 // information from the source event) breaks this project's build instead of
 // silently emitting warnings.
diff --git a/tests/TUnit.Mocks.Tests/NullLiteralMatcherTests.cs b/tests/TUnit.Mocks.Tests/NullLiteralMatcherTests.cs
new file mode 100644
index 0000000000..14017c1fad
--- /dev/null
+++ b/tests/TUnit.Mocks.Tests/NullLiteralMatcherTests.cs
@@ -0,0 +1,82 @@
+namespace TUnit.Mocks.Tests;
+
+public interface INullLiteralService
+{
+    string Take(string? value);
+    string Pair(string? first, string? second);
+    void Notify(string? value);
+    string NullableNumber(int? value);
+    string Number(int value);
+    string GenericNumber<T>(T value);
+}
+
+public class NullLiteralMatcherTests
+{
+    [Test]
+    public async Task Default_Literal_For_NonNullable_Number_Matches_Zero()
+    {
+        var mock = Mock.Of<INullLiteralService>();
+        mock.Number(default).Returns("zero");
+
+        await Assert.That(mock.Object.Number(0)).IsEqualTo("zero");
+        await Assert.That(mock.Object.Number(1)).IsEqualTo("");
+
+        mock.Number(default).WasCalled(Times.Once);
+        mock.Number(default(int)).WasCalled(Times.Once);
+    }
+
+    [Test]
+    public async Task Default_Literal_For_Generic_Parameter_Matches_Its_Default_Value()
+    {
+        var mock = Mock.Of<INullLiteralService>();
+        mock.GenericNumber<int>(default).Returns("zero");
+        mock.GenericNumber<string?>(default).Returns("null");
+
+        await Assert.That(mock.Object.GenericNumber(0)).IsEqualTo("zero");
+        await Assert.That(mock.Object.GenericNumber(1)).IsEqualTo("");
+        await Assert.That(mock.Object.GenericNumber<string?>(null)).IsEqualTo("null");
+        await Assert.That(mock.Object.GenericNumber<string?>("value")).IsEqualTo("");
+
+        mock.GenericNumber<int>(default).WasCalled(Times.Once);
+        mock.GenericNumber<string?>(default).WasCalled(Times.Once);
+    }
+
+    [Test]
+    public async Task Null_And_Default_Literals_Match_Only_Null()
+    {
+        var mock = Mock.Of<INullLiteralService>();
+        mock.Take(null).Returns("null");
+        mock.NullableNumber(default).Returns("null number");
+        mock.Notify(default).WasNeverCalled();
+
+        await Assert.That(mock.Object.Take(null)).IsEqualTo("null");
+        await Assert.That(mock.Object.Take("value")).IsEqualTo("");
+        await Assert.That(mock.Object.NullableNumber(null)).IsEqualTo("null number");
+        await Assert.That(mock.Object.NullableNumber(1)).IsEqualTo("");
+        mock.Object.Notify(null);
+        mock.Object.Notify("value");
+
+        mock.Take(default).WasCalled(Times.Once);
+        mock.NullableNumber(null).WasCalled(Times.Once);
+        mock.Notify(null).WasCalled(Times.Once);
+    }
+
+    [Test]
+    public async Task Null_Literals_Combine_With_Predicates_And_Exact_Values()
+    {
+        var mock = Mock.Of<INullLiteralService>();
+        mock.Pair(null, value => value == "second").Returns("first null");
+        mock.Pair(value => value == "first", default).Returns("second null");
+        mock.Pair(null, "exact").Returns("exact");
+        mock.Pair(null, null).Returns("both null");
+
+        await Assert.That(mock.Object.Pair(null, "second")).IsEqualTo("first null");
+        await Assert.That(mock.Object.Pair("first", null)).IsEqualTo("second null");
+        await Assert.That(mock.Object.Pair(null, "exact")).IsEqualTo("exact");
+        await Assert.That(mock.Object.Pair(null, null)).IsEqualTo("both null");
+        await Assert.That(mock.Object.Pair("other", "second")).IsEqualTo("");
+        mock.Pair(null, value => value == "second").WasCalled(Times.Once);
+        mock.Pair(value => value == "first", default).WasCalled(Times.Once);
+        mock.Pair(default, default).WasCalled(Times.Once);
+    }
+}
diff --git a/tests/TUnit.Mocks.Tests/TUnit.Mocks.Tests.csproj b/tests/TUnit.Mocks.Tests/TUnit.Mocks.Tests.csproj
index 3f5aa87fc6..c6bed4eb7c 100644
--- a/tests/TUnit.Mocks.Tests/TUnit.Mocks.Tests.csproj
+++ b/tests/TUnit.Mocks.Tests/TUnit.Mocks.Tests.csproj
@@ -9,8 +9,9 @@
   </PropertyGroup>
 
   <PropertyGroup>
+    <!-- Enforce null-literal and generated event nullability regression coverage. -->
+    <WarningsAsErrors>$(WarningsAsErrors);CS8625;CS8604;CS8612;CS8613;CS8614;CS8615;CS8634</WarningsAsErrors>
     <SignAssembly>true</SignAssembly>
-    <WarningsAsErrors>$(WarningsAsErrors);CS8604;CS8612;CS8613;CS8614;CS8615;CS8634</WarningsAsErrors>
     <AssemblyOriginatorKeyFile>..\..\eng\strongname.snk</AssemblyOriginatorKeyFile>
   </PropertyGroup>