Fix for issue 40774 RequestDelegateFactory null param default (#41025)

Author: Acerby

src/Http/Http.Extensions/src/RequestDelegateFactory.cs

@@ -1132,7 +1132,7 @@ private static Expression BindParameterFromValue(ParameterInfo parameter, Expres
             ? Expression.IfThen(TempSourceStringNotNullExpr, tryParseExpression)
             : Expression.IfThenElse(TempSourceStringNotNullExpr, tryParseExpression,
                 Expression.Assign(argument,
-                Expression.Constant(parameter.DefaultValue)));
+                Expression.Constant(parameter.DefaultValue, parameter.ParameterType)));
 
         var loopExit = Expression.Label();
 

src/Http/Http.Extensions/test/RequestDelegateFactoryTests.cs

@@ -226,6 +226,11 @@ private static void TestOptionalNullable(HttpContext httpContext, int? value = 4
         httpContext.Items.Add("input", value);
     }
 
+    private static void TestOptionalNullableNull(HttpContext httpContext, double? value = null)
+    {
+        httpContext.Items.Add("input", (object?)value ?? "Null");
+    }
+
     private static void TestOptionalString(HttpContext httpContext, string value = "default")
     {
         httpContext.Items.Add("input", value);
@@ -364,13 +369,26 @@ public async Task RequestDelegatePopulatesFromNullableOptionalParameter()
     {
         var httpContext = CreateHttpContext();
 
-        var factoryResult = RequestDelegateFactory.Create(TestOptional);
+        var factoryResult = RequestDelegateFactory.Create(TestOptionalNullable);
         var requestDelegate = factoryResult.RequestDelegate;
 
         await requestDelegate(httpContext);
 
         Assert.Equal(42, httpContext.Items["input"]);
     }
+    
+    [Fact]
+    public async Task RequestDelegatePopulatesFromNullableNullOptionalParameter()
+    {
+        var httpContext = CreateHttpContext();
+
+        var factoryResult = RequestDelegateFactory.Create(TestOptionalNullableNull);
+        var requestDelegate = factoryResult.RequestDelegate;
+
+        await requestDelegate(httpContext);
+
+        Assert.Equal("Null", httpContext.Items["input"]);
+    }
 
     [Fact]
     public async Task RequestDelegatePopulatesFromOptionalStringParameter()