Since some minutes all open patches and postmerge builds are failing with inintelligible error messages like those at https://integration.wikimedia.org/ci/job/mwext-phpunit-coverage-docker-publish/1412/console. As such, I cannot add much more details as I don't know what's the cause. The result is that https://gerrit.wikimedia.org/r/#/q/status:open are all failing.
```
17:18:34 Digest: sha256:0e16c30b9b41b55f7c3129d5e5b0e3d0867a8068863cbeec8f4ecafa3a290843
17:18:34 Status: Downloaded newer image for docker-registry.wikimedia.org/releng/quibble-stretch:0.0.22
17:18:35 DEBUG:quibble.cmd:Running stages:
17:18:35 DEBUG:quibble.cmd:ZUUL_PROJECT=mediawiki/extensions/StopForumSpam
17:18:35 INFO:quibble.cmd:Projects: mediawiki/core, mediawiki/skins/Vector, mediawiki/extensions/StopForumSpam, mediawiki/extensions/AbuseFilter, mediawiki/extensions/AntiSpoof, mediawiki/extensions/CheckUser, mediawiki/extensions/CodeEditor, mediawiki/extensions/EventLogging, mediawiki/extensions/WikiEditor
17:18:35 Traceback (most recent call last):
17:18:35 File "/usr/local/bin/quibble", line 11, in <module>
17:18:35 load_entry_point('quibble==0.0.0', 'console_scripts', 'quibble')()
17:18:35 File "/usr/local/lib/python3.5/dist-packages/quibble/cmd.py", line 528, in main
17:18:35 cmd.execute()
17:18:35 File "/usr/local/lib/python3.5/dist-packages/quibble/cmd.py", line 412, in execute
17:18:35 self.clone(projects_to_clone)
17:18:35 File "/usr/local/lib/python3.5/dist-packages/quibble/cmd.py", line 216, in clone
17:18:35 cache_dir=self.args.git_cache)
17:18:35 File "/usr/local/lib/python3.5/dist-packages/quibble/zuul.py", line 47, in clone
17:18:35 for x in project_branch:
17:18:35 TypeError: 'NoneType' object is not iterable
17:18:35 Build step 'Execute shell' marked build as failure
```