diff --git a/ChangeLog.md b/ChangeLog.md
index 8426b98297..228d75099a 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -26,7 +26,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - [CLI] Fix filtering of projects (relates to `--projects` or `--ignored-projects` parameter) ([#914](https://github.com/josefpihrt/roslynator/pull/914)).
 - Refactoring "Add using directive" (RR0014) now works when file-scoped namespace is used ([#932](https://github.com/josefpihrt/roslynator/pull/932)).
 - Add parentheses if necessary in a code fix for [RCS1197](https://github.com/JosefPihrt/Roslynator/blob/main/docs/analyzers/RCS1197.md) ([#928](https://github.com/josefpihrt/roslynator/pull/928) by @karl-sjogren).
-- Do not simplify default expression if it would change semantics [RCS1244](https://github.com/JosefPihrt/Roslynator/blob/main/docs/analyzers/RCS1244.md) ([#939](https://github.com/josefpihrt/roslynator/pull/939).
+- Do not simplify default expression if it would change semantics ([RCS1244](https://github.com/JosefPihrt/Roslynator/blob/main/docs/analyzers/RCS1244.md)) ([#939](https://github.com/josefpihrt/roslynator/pull/939).
+- Fix NullReferenceException in [RCS1198](https://github.com/JosefPihrt/Roslynator/blob/main/docs/analyzers/RCS1198.md) ([#940](https://github.com/josefpihrt/roslynator/pull/940).
 
 -----
 <!-- Content below does not adhere to 'Keep a Changelog' format -->
diff --git a/src/Analyzers/CSharp/Analysis/AvoidBoxingOfValueTypeAnalysis.cs b/src/Analyzers/CSharp/Analysis/AvoidBoxingOfValueTypeAnalysis.cs
index b8308df0ea..8204208fe6 100644
--- a/src/Analyzers/CSharp/Analysis/AvoidBoxingOfValueTypeAnalysis.cs
+++ b/src/Analyzers/CSharp/Analysis/AvoidBoxingOfValueTypeAnalysis.cs
@@ -40,7 +40,7 @@ public static void Analyze(SyntaxNodeAnalysisContext context, in SimpleMemberInv
 
                                 if (!expression.IsKind(SyntaxKind.InterpolatedStringExpression, SyntaxKind.AddExpression)
                                     && parameters[0].Type.IsObject()
-                                    && context.SemanticModel.GetTypeSymbol(expression, context.CancellationToken).IsValueType)
+                                    && context.SemanticModel.GetTypeSymbol(expression, context.CancellationToken)?.IsValueType == true)
                                 {
                                     DiagnosticHelpers.ReportDiagnostic(context, DiagnosticRules.AvoidBoxingOfValueType, argument);
                                     return;
diff --git a/src/Tests/Analyzers.Tests/RCS1198AvoidBoxingOfValueTypeTests2.cs b/src/Tests/Analyzers.Tests/RCS1198AvoidBoxingOfValueTypeTests2.cs
index 20482e3ef7..c8b8343827 100644
--- a/src/Tests/Analyzers.Tests/RCS1198AvoidBoxingOfValueTypeTests2.cs
+++ b/src/Tests/Analyzers.Tests/RCS1198AvoidBoxingOfValueTypeTests2.cs
@@ -100,6 +100,26 @@ void M()
         sb.AppendFormat(""f"", i, i, i, i);
     }
 }
+");
+        }
+
+        [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.AvoidBoxingOfValueType)]
+        public async Task TestNoDiagnostic_NoTypeSymbol()
+        {
+            await VerifyNoDiagnosticAsync(@"
+using System.Text;
+
+class C
+{
+    void M()
+    {
+        var f = false;
+
+        var sb = new StringBuilder();
+
+        sb.Append(f ? ""ab"" : 'c');
+    }
+}
 ");
         }
     }