pytorch

28c51996 - Follow the undefined Tensor <-> None rule better in torch dispatch (#67793)

Follow the undefined Tensor <-> None rule better in torch dispatch (#67793) Summary: As per title. This in particular allows to more easily override backward function for which the underlying backend returns `None` Pull Request resolved: https://github.com/pytorch/pytorch/pull/67793 Reviewed By: zou3519 Differential Revision: D32242962 Pulled By: albanD fbshipit-source-id: 6e114def90ee9499161e1303d301ba7fd003ff89