GitLab

There was a bug where if the ID were passed as null or undefined (rather
than completely omitted), the message would fail to parse. Fix this, and
add a unittest.

Bug: 828664

Change-Id: I92b0f071a1627322e12e8eaf0f5787ccd0793138
Reviewed-on: https://chromium-review.googlesource.com/1012601Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550718}