Starter Task 1 (#64927)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/64927
Mypy error corrections
Test Plan: Corrected mypy errors to make code less prone to bugs by modifying types or adding lines that avoid special undesired cases e.g. asserting a variable to not None.
Reviewed By: wushirong
Differential Revision: D30901654
fbshipit-source-id: daae8692603b8b38203a98f673c455749c2fb855
