Correct PHPDoc or add default return for numerous methods
Summary:
Correct PHPDoc when none of the method calls try to handle a return value.
Add missing fallback `return` statements (which may never be reached if previous condition checks were always true).
This reduces the amount of errors reported by static code analysis tools.
Test Plan: Carefully read the code and check all places in which a function gets called whether a return value is expected.
Reviewers: O1 Blessed Committers, valerio.bozzolan
Reviewed By: O1 Blessed Committers, valerio.bozzolan
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Differential Revision: https://we.phorge.it/D25650