Comment 35 for bug 1769383

Sorry, i missed comment #29, but there are a lot of bug reports out there, some of them over a year old, which describe the same issue.

My reproduction steps, tested on a virtualbox machine:

1) Fresh-Install Ubuntu 18.0.4.1 LTS
2) Install package 'chrome-gnome-shell'
3) Navigate to https://extensions.gnome.org/extension/307/dash-to-dock, install firefox/chrome extension and install dash-to-dock extension.
4) Restart
5) On next lock the ubuntu-dock reappears and the following journalctl /usr/bin/gnome-shell output is generated:

Nov 15 12:53:15 ubuntu gnome-shell[1143]: Extension "<email address hidden>" had error: TypeError: dockManager is null

The suggested fix is resolving this and a quick look into https://git.launchpad.net/ubuntu/+source/gnome-shell-extension-ubuntu-dock/tree/extension.js?h=ubuntu/bionic exposes, that the issue is a simple missing null-check in the disable() function where dockManager.destroy() is called on a null-instance, which should be added in either way.