Fix fatal in Maniphest

Summary:
Fixes T9596.

Was unable to navigate to a task in Maniphest.

Test Plan: navigate to that task.

Reviewers: #blessed_reviewers, epriestley, avivey, tycho.tatitscheff

Reviewed By: avivey, tycho.tatitscheff

Subscribers: tycho.tatitscheff, avivey, Korvin

Maniphest Tasks: T9596

Differential Revision: https://secure.phabricator.com/D14300