Replace a few null return values with void for consistency
Summary: These private functions are not supposed to return anything as their return value is never read anyway, thus consistently return void instead of null (which makes no technical difference but is easier to read).
Test Plan: Look at the other return values in the same function, and the calls of the function.
Reviewers: O1 Blessed Committers, mainframe98
Reviewed By: O1 Blessed Committers, mainframe98
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Differential Revision: https://we.phorge.it/D26666