Fix VbNameExpander corrupting open generic types like GetType(Nullable(Of))

Roslyn's Simplifier.Expand replaces missing type arguments (open generics like
Nullable(Of)) with an error type fallback (Object), causing GetType(Nullable(Of))
to incorrectly convert to typeof(object) instead of typeof(Nullable<>).

Guard against this in NameCanBeExpanded by detecting GenericNameSyntax nodes with
missing type arguments and skipping expansion, preserving the open generic form so
the conversion visitors can correctly emit OmittedTypeArgument.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: GrahamTheCoder

CodeConverter/CSharp/VbNameExpander.cs

@@ -110,6 +110,9 @@ private static bool NameCanBeExpanded(SyntaxNode node)
         if (node.Parent is NameColonEqualsSyntax || node.Parent is NamedFieldInitializerSyntax) return false;
         // Workaround roslyn bug where it duplicates the inferred name
         if (node.Parent is InferredFieldInitializerSyntax) return false;
+        // Roslyn's Simplifier.Expand corrupts open generic type arguments (e.g. Nullable(Of) in GetType(Nullable(Of)))
+        // by replacing them with the error type fallback (Object). Prevent expansion so the missing type arg is preserved.
+        if (node is GenericNameSyntax gns && gns.TypeArgumentList.Arguments.Any(a => a is IdentifierNameSyntax id && id.Identifier.IsMissing)) return false;
         return true;
     }
 

Tests/CSharp/ExpressionTests/OmittedTypeArgumentTest.cs

@@ -16,9 +16,9 @@ Return type.IsGenericType AndAlso type.GetGenericTypeDefinition() Is GetType(Nul
     End Function
 End Class", @"using System;
 
-public class Test
+public partial class Test
 {
-    public bool IsNullable(Type type)
+    public bool IsNullable(Type @type)
     {
         return type.IsGenericType && ReferenceEquals(type.GetGenericTypeDefinition(), typeof(Nullable<>));
     }