Diffusion - fix T3215

Summary: Ref T2784. We need to always return array() here so the foreach doesn't crap out

Test Plan: chad - can you confirm this fixes the error? I have ref-heavy git repos it seems. should work though.

Reviewers: chad, epriestley

Reviewed By: chad

CC: aran, Korvin

Maniphest Tasks: T3215, T2784

Differential Revision: https://secure.phabricator.com/D5961