improve error msg when module list isn't added to __constants__ (#17167)
Summary:
Add suggestion to add to __constants__ when a ModuleList of Sequential module is used as a tuple
Addresses https://github.com/pytorch/pytorch/issues/13899
Pull Request resolved: https://github.com/pytorch/pytorch/pull/17167
Differential Revision: D14107688
Pulled By: eellison
fbshipit-source-id: 8c07d1f3e25a9c6bdcfd96dbf6b72c2130838278
