C#: Use cast expressions for object defaults.

Author: michaelnebel

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expression.cs

@@ -202,16 +202,6 @@ private static bool ContainsPattern(SyntaxNode node) =>
                 return Default.CreateGenerated(cx, parent, childIndex, location, parameter.Type.IsReferenceType ? ValueAsString(null) : null);
             }
 
-            if (parameter.Type.SpecialType is SpecialType.System_Object)
-            {
-                // this can happen in VB.NET
-                cx.ExtractionError($"Extracting default argument value 'object {parameter.Name} = default' instead of 'object {parameter.Name} = {defaultValue}'. The latter is not supported in C#.",
-                    null, null, severity: Semmle.Util.Logging.Severity.Warning);
-
-                // we're generating a default expression:
-                return Default.CreateGenerated(cx, parent, childIndex, location, ValueAsString(null));
-            }
-
             if (type.SpecialType is SpecialType.None)
             {
                 return ImplicitCast.CreateGeneratedConversion(cx, parent, childIndex, type, defaultValue, location);
@@ -222,7 +212,9 @@ private static bool ContainsPattern(SyntaxNode node) =>
                 return DateTimeObjectCreation.CreateGenerated(cx, parent, childIndex, type, defaultValue, location);
             }
 
-            if (type.SpecialType is SpecialType.System_IntPtr || type.SpecialType is SpecialType.System_UIntPtr)
+            if (type.SpecialType is SpecialType.System_Object ||
+                type.SpecialType is SpecialType.System_IntPtr ||
+                type.SpecialType is SpecialType.System_UIntPtr)
             {
                 return ImplicitCast.CreateGenerated(cx, parent, childIndex, type, defaultValue, location);
             }