Minor fix presumably identified by PHPStan
Summary: Address comments from @vrana, see D14512#207302.
Test Plan: Ran unit tests.
Reviewers: epriestley, Blessed Reviewers
Reviewed By: epriestley, Blessed Reviewers
Subscribers: Korvin, Firehed, vrana
Differential Revision: https://secure.phabricator.com/D17435