Broken in 0.8, nullable instance produces missing declaration
I'm working on a reproducer; meanwhile, see the lobby chat from [here](https://gitter.im/kaitai_struct/Lobby?at=5a80faf118f388e6268f8c59) to [here](https://gitter.im/kaitai_struct/Lobby?at=5a81946cf283b8e5464f7b80).