fix optional type subtype relation (#22186)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22186
ghimport-source-id: 05ef8c3a176fe2a67d4835888e6db52b57a6d199
Test Plan: Imported from OSS
Differential Revision: D15994644
Pulled By: wanchaol
fbshipit-source-id: 7c5c4eebd421f6c9470661c2c2eb38bafdff8bbd
