Summary: Ref T6203. Ref T13661. These policies are incorrectly nullable, although it's likely that no pathway exists in the application to write NULL into them. Fix the schema.
Test Plan: Ran `bin/storage upgrade`.
Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam
Maniphest Tasks: T13661, T6203
Differential Revision: https://secure.phabricator.com/D21748
