This error happens when setting up a new wiki on https://patchdemo.wmflabs.org/, when running the edit.php maintenance script:
TypeError: Argument 1 passed to Wikimedia\Rdbms\TransactionProfiler::recordConnection() must be of the type string, null given, called in /srv/patchdemo-wikis/78374bbd8ec1152e7332eda02d0f3ff7/w/includes/libs/rdbms/loadbalancer/LoadBalancer.php on line 1006 Backtrace: from /srv/patchdemo-wikis/78374bbd8ec1152e7332eda02d0f3ff7/w/includes/libs/rdbms/TransactionProfiler.php(197) #0 /srv/patchdemo-wikis/78374bbd8ec1152e7332eda02d0f3ff7/w/includes/libs/rdbms/loadbalancer/LoadBalancer.php(1006): Wikimedia\Rdbms\TransactionProfiler->recordConnection(NULL, string, boolean) #1 /srv/patchdemo-wikis/78374bbd8ec1152e7332eda02d0f3ff7/w/includes/libs/rdbms/loadbalancer/LoadBalancer.php(960): Wikimedia\Rdbms\LoadBalancer->getServerConnection(integer, string, integer) #2 /srv/patchdemo-wikis/78374bbd8ec1152e7332eda02d0f3ff7/w/includes/libs/rdbms/loadbalancer/LoadBalancer.php(1099): Wikimedia\Rdbms\LoadBalancer->getConnection(integer, array, string, integer) #3 /srv/patchdemo-wikis/78374bbd8ec1152e7332eda02d0f3ff7/w/includes/user/User.php(819): Wikimedia\Rdbms\LoadBalancer->getConnectionRef(integer) #4 /srv/patchdemo-wikis/78374bbd8ec1152e7332eda02d0f3ff7/w/maintenance/edit.php(64): User::newSystemUser(string, array) #5 /srv/patchdemo-wikis/78374bbd8ec1152e7332eda02d0f3ff7/w/maintenance/doMaintenance.php(112): EditCLI->execute() #6 /srv/patchdemo-wikis/78374bbd8ec1152e7332eda02d0f3ff7/w/maintenance/edit.php(134): require_once(string) #7 {main}