For example: https://secure.phabricator.com/tag/wikimedia/
>>> UNRECOVERABLE FATAL ERROR <<< Call to a member function getBuiltinKey() on a non-object /core/lib/phabricator/src/applications/project/controller/PhabricatorProjectViewController.php:23 ┻━┻ ︵ ¯\_(ツ)_/¯ ︵ ┻━┻
The project works just fine if you visit https://secure.phabricator.com/project/manage/404/
I tried to work around the immediate fatal by checking the return value of $engine->getDefaultItem() in PhabricatorProjectViewController, however, that resulted in hitting a 404 so it's a bit deeper of an issue. Perhaps the right solution is to prevent users from disabling both of the default items in the project "manage menu" UI?
D18836 probably isn't the right solution, however, it's the only straightforward fix I could come up with. I didn't dig into the details of why it 404s when I fix the code in PhabricatorProjectViewController to avoid the fatal. The patch is probably good enough for Wikimedia, however, I'm not sure if it's good enough for upstream.