Revert "Revert "Revert "Correct nullability and final constraints on new APIs."""

This reverts commit b255be13.

Reason for revert: the commit being reverted fixed git_master but broke aosp-master. This revert is aimed to fix aosp-master while not touching git_master.

DO NOT MERGE: This change is aimed at aosp-master only and should not be merged into git_master.

Change-Id: Ie5aaabb211affe2d21daaf87809641276d9d4707