Check for None in torch.jit.Graph.create (#68253)
Summary:
...because we don't like segfaults from Python (see test).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/68253
Reviewed By: suo
Differential Revision: D32396747
Pulled By: gmagogsfm
fbshipit-source-id: a0925e8479702766e88176280985a63bc79e4f6a
