[C#] Failed to generate Verifier for Union type [flatc version 23.5.26]

[KotoriK]

Brief

affected language: C#,csharp
flatc version 23.5.26
flatc option: -n --gen-onefile

Test Schema

namespace Test;
table A{
    a:string;
}
table B{
    b:uint;
}
union Un{
    A,
    B
}
table T{
    u:Un;
}
root_type T;

Generated Code Snippet

static public class TVerify
{
  static public bool Verify(Google.FlatBuffers.Verifier verifier, uint tablePos)
  {
    return verifier.VerifyTableStart(tablePos)
      && verifier.VerifyField(tablePos, 4 /*UType*/, 1 /*Test.Un*/, 1, false)
      && verifier.VerifyUnion(tablePos, 4, 6 /*U*/, Test.UnVerify.Verify, false) // Test.UnVerify is referenced here but not defined anywhere
      && verifier.VerifyTableEnd(tablePos);
  }
}

Expected behaviour

Define Test.UnVerify.Verify in flatc generated code.