Nothing is the default, don't bother specifying since we can't get it right for structs - fixes #1056

Author: GrahamTheCoder

CodeConverter/CSharp/ExpressionNodeVisitor.cs

@@ -1408,10 +1408,12 @@ public override async Task<CSharpSyntaxNode> VisitParameter(VBSyntax.ParameterSy
                 var arg = CommonConversions.CreateAttributeArgumentList(SyntaxFactory.AttributeArgument(defaultExpression));
                 _extraUsingDirectives.Add("System.Runtime.InteropServices");
                 _extraUsingDirectives.Add("System.Runtime.CompilerServices");
-                var optionalAttributes = new[] {
+                var optionalAttributes = new List<AttributeSyntax> {
                     SyntaxFactory.Attribute(SyntaxFactory.IdentifierName("Optional")),
-                    SyntaxFactory.Attribute(SyntaxFactory.IdentifierName("DefaultParameterValue"), arg)
                 };
+                if (!node.Default.Value.IsKind(VBasic.SyntaxKind.NothingLiteralExpression)) {
+                    optionalAttributes.Add(SyntaxFactory.Attribute(SyntaxFactory.IdentifierName("DefaultParameterValue"), arg));
+                }
                 attributes.Insert(0,
                     SyntaxFactory.AttributeList(SyntaxFactory.SeparatedList(optionalAttributes)));
             } else {

Tests/CSharp/ExpressionTests/ByRefTests.cs

@@ -347,9 +347,9 @@ public static bool CallingFunc()
     public async Task RefAfterOptionalArgumentAsync()
     {
         await TestConversionVisualBasicToCSharpAsync(@"
-    Sub S(Optional a As Integer = 0, Optional ByRef b As Integer = 0)
-        S()
-    End Sub
+Sub S(Optional a As Integer = 0, Optional ByRef b As Integer = 0)
+    S()
+End Sub
 ", @"
 public void S([Optional, DefaultParameterValue(0)] int a, [Optional, DefaultParameterValue(0)] ref int b)
 {
@@ -358,6 +358,18 @@ public void S([Optional, DefaultParameterValue(0)] int a, [Optional, DefaultPara
 }");
     }
 
+    [Fact]
+    public async Task DateRefAfterOptionalArgumentAsync()
+    {
+        await TestConversionVisualBasicToCSharpAsync(@"
+Sub S(Optional ByRef dt As Date = Nothing)
+End Sub
+", @"
+public void S([Optional] ref DateTime dt)
+{
+}");
+    }
+
     [Fact]
     public async Task OutOptionalArgumentAsync()
     {
@@ -378,7 +390,7 @@ End Sub
 
 public partial class OptionalOutIssue882
 {
-    private void TestSub(out int a, [Optional, DefaultParameterValue(default(int))] out int b)
+    private void TestSub(out int a, [Optional] out int b)
     {
         a = 42;
         b = 23;