Cannot read property 'mentionableUsers' of null

[smashwilson]

Prerequisites

• Have you tried to reproduce the problem in Safe Mode?
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Description

We seem to have a stack in the dev console on launch:

Uncaught (in promise) TypeError: Cannot read property 'mentionableUsers' of null
    at UserStore.loadMentionableUsers (/Applications/Atom Dev.app/Contents/Resources/app/static/<embedded>:14:3904824)
    at <anonymous>

Steps to Reproduce

1. Open Atom on a project folder that's a git repository with a GitHub remote. I see this on atom/github.

Expected behavior:

A clean dev console.

Actual behavior:

The error ☝️ appears as soon as the github package is activated. (You don't need to open the Git or GitHub tabs, even.)

Reproduces how often:

100%

Versions

$ atom-dev --version
Atom    : 1.35.0-dev-3a046f511
Electron: 2.0.16
Chrome  : 61.0.3163.100
Node    : 8.9.3
$ apm --version
apm  2.1.3
npm  6.2.0
node 8.9.3 x64
atom 1.35.0-nightly10
python 2.7.15
git 2.20.1

Additional Information

Please include any additional information, configuration or data that might be necessary to reproduce the issue. Screenshots, if appropriate, are helpful as well.

If your issue involves a repository, and that repository is public, please include a link to it.