Fix call to debug.log.

Summary: As pointed out by @epriestley in D9458#62, this call to debug.log is missing an argument.

Test Plan: meh..

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D9485