Fix getConstant (#31012)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31012
- getConstant should throw when the item is not found
- add another getConstant which takes slot index as argument
Test Plan:
test_class_type.cpp
Imported from OSS
Differential Revision: D18898418
fbshipit-source-id: d3a23a4896fdbf5fa98e1c55c9c4d6205840014b
