Since I did not want to start the new year with software that isn’t up-to-date (or because I had a little time and didn’t want to do any real work), I decided to update my ownCloud installation to version 8.2.2. Unfortunately, the update tool failed:

Fatal error: Call to a member function getLogger() on a non-object in /path/to/owncloud/lib/public/util.php on line 166

After spending some time trying various stuff, I decided to compare my installation with a fresh one. The only thing I found that was weird was that I had a config.php in the main ownCloud directory (probably left over from a manual update I did a few months back).

So I renamed that one – and voilà. Apparently having a config.php in the main folder causes ownCloud to stop working.
I write this because I didn’t find any solutions of this problem online when I searched.