[Bug][compiler-v2] Enum constructors without arguments don't work in expressions

[wrwg]

The following does not work as expected:

  enum MessageHolder has key, drop {
        Empty,
        Message{
           message: string::String,
        }
    }

   fun expect_value(): MessageHolder {
       MessageHolder::Empty // <--- should work but doesn't, and gives misleading error message
       // MessageHolder::Empty{} // <-- does work
   }