The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/a861f6af30de2c7dc9511972469694059ddfd168

commit a861f6af30de2c7dc9511972469694059ddfd168
Author: Brandon Wylie <wylieb@chromium.org>
Date: Wed Mar 07 01:34:38 2018

[CTF] Fix error for null occurrence

Bug:819424
Change-Id: I96f0a1b6dc11843ded0227ae384c7d3933282cf6
Reviewed-on: https://chromium-review.googlesource.com/952479
Reviewed-by: Shuotao Gao <stgao@chromium.org>
Commit-Queue: Brandon Wylie <wylieb@chromium.org>

[modify] https://crrev.com/a861f6af30de2c7dc9511972469694059ddfd168/appengine/chromium_try_flakes/handlers/flake_issues.py