Summary:
Gone trough all the FIXMEs added in the previous diff by the nullsafe tool, marked the class as nullsafe and ensured no remaining violations.
Changelog: [Android][Fixed] Made ModuleHolder.java nullsafe
Reviewed By: alanleedev
Differential Revision: D72384056
fbshipit-source-id: 42bfdd9b73bdb599ab67b6fe8759c80665156d22