Address review: move char/empty comparison to TryConvertToNullOrEmptyCheck

Move the root cause fix (char vs empty string comparison) from
BinaryExpressionConverter into VisualBasicEqualityComparison.TryConvertToNull
OrEmptyCheck, which is the natural home for all null/empty comparison rewrites.
This also correctly handles OptionCompareText (char comparison is never
text-sensitive so it runs before the OptionCompareTextCaseInsensitive bail-out).

https://claude.ai/code/session_01AkwUvu3XuCdj3D4axoX4UX

Author: claude

CodeConverter/CSharp/BinaryExpressionConverter.cs

@@ -87,16 +87,6 @@ private async Task<CSharpSyntaxNode> ConvertBinaryExpressionAsync(VBasic.Syntax.
                 }
                 if (lhsTypeInfo.Type?.SpecialType == SpecialType.System_Char && rhsTypeInfo.Type?.SpecialType == SpecialType.System_Char) {
                     // Do nothing, char comparison
-                } else if (!_visualBasicEqualityComparison.OptionCompareTextCaseInsensitive &&
-                           ((lhsTypeInfo.Type?.SpecialType == SpecialType.System_Char && rhsTypeInfo.Type?.SpecialType == SpecialType.System_String && _visualBasicEqualityComparison.IsNothingOrEmpty(node.Right)) ||
-                            (rhsTypeInfo.Type?.SpecialType == SpecialType.System_Char && lhsTypeInfo.Type?.SpecialType == SpecialType.System_String && _visualBasicEqualityComparison.IsNothingOrEmpty(node.Left)))) {
-                    if (lhsTypeInfo.Type?.SpecialType == SpecialType.System_Char) {
-                        rhs = CS.SyntaxFactory.MemberAccessExpression(CS.SyntaxKind.SimpleMemberAccessExpression, CS.SyntaxFactory.PredefinedType(CS.SyntaxFactory.Token(CS.SyntaxKind.CharKeyword)), CS.SyntaxFactory.IdentifierName("MinValue"));
-                        omitConversion = true;
-                    } else {
-                        lhs = CS.SyntaxFactory.MemberAccessExpression(CS.SyntaxKind.SimpleMemberAccessExpression, CS.SyntaxFactory.PredefinedType(CS.SyntaxFactory.Token(CS.SyntaxKind.CharKeyword)), CS.SyntaxFactory.IdentifierName("MinValue"));
-                        omitConversion = true;
-                    }
                 } else {
                     (lhs, rhs) = _visualBasicEqualityComparison.AdjustForVbStringComparison(node.Left, lhs, lhsTypeInfo, false, node.Right, rhs, rhsTypeInfo, false);
                     omitConversion = true; // Already handled within for the appropriate types (rhs can become int in comparison)

CodeConverter/CSharp/VisualBasicEqualityComparison.cs

@@ -180,19 +180,31 @@ private static ObjectCreationExpressionSyntax NewStringFromArg(ExpressionSyntax
     public bool TryConvertToNullOrEmptyCheck(VBSyntax.BinaryExpressionSyntax node, ExpressionSyntax lhs,
         ExpressionSyntax rhs, TypeInfo lhsTypeInfo, TypeInfo rhsTypeInfo, out CSharpSyntaxNode? visitBinaryExpression)
     {
-        if (OptionCompareTextCaseInsensitive)
-        {
-            visitBinaryExpression = null;
-            return false;
-        }
-
         bool lhsEmpty = IsNothingOrEmpty(node.Left);
         bool rhsEmpty = IsNothingOrEmpty(node.Right);
 
         if (lhsEmpty || rhsEmpty)
         {
             var arg = lhsEmpty ? rhs : lhs;
             var argType = lhsEmpty ? rhsTypeInfo : lhsTypeInfo;
+
+            if (argType.Type?.SpecialType == SpecialType.System_Char) {
+                // char = "" in VB means char == '\0' (char.MinValue) in C#; not affected by OptionCompareText
+                var charMinValue = SyntaxFactory.MemberAccessExpression(SyntaxKind.SimpleMemberAccessExpression,
+                    SyntaxFactory.PredefinedType(SyntaxFactory.Token(SyntaxKind.CharKeyword)),
+                    ValidSyntaxFactory.IdentifierName("MinValue"));
+                var equalityKind = node.IsKind(VBasic.SyntaxKind.NotEqualsExpression) ? SyntaxKind.NotEqualsExpression : SyntaxKind.EqualsExpression;
+                var opToken = SyntaxFactory.Token(node.IsKind(VBasic.SyntaxKind.NotEqualsExpression) ? SyntaxKind.ExclamationEqualsToken : SyntaxKind.EqualsEqualsToken);
+                visitBinaryExpression = SyntaxFactory.BinaryExpression(equalityKind, arg, opToken, charMinValue);
+                return true;
+            }
+
+            if (OptionCompareTextCaseInsensitive)
+            {
+                visitBinaryExpression = null;
+                return false;
+            }
+
             if (argType.Type?.SpecialType != SpecialType.System_String && argType.Type?.SpecialType != SpecialType.System_Object) {
                 visitBinaryExpression = null;
                 return false;