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