RNN-T: Strange type in forward LSTMDropout
Good catch. I was trying our a few things with decoupled lstms and forgot to update signature. 
https://github.com/NVIDIA/NeMo/blob/297a8bdbb0370a51cb74a41288025befd9cd2392/nemo/collections/common/parts/rnn.py#L196

@titu1994, why does `h` have this type? I suppose it should be `Optional[[Tuple[torch.Tensor, torch.Tensor]]`, just like returnable `h`