The execution of "php /srv/www/balloon/src/cgi-bin/cli.php upgrade -vvv" ends with:
[2019-09-10T13:24:03.741315+00:00] default.EMERGENCY: uncaught exception: Return value of Balloon\Migration\Delta\CreateUniqueUserMailIndex::createIndex() must be of the type string, none returned {"category":"Balloon\Bootstrap\Cli","exception":"[object] (TypeError(code: 0): Return value of Balloon\Migration\Delta\CreateUniqueUserMailIndex::createIndex() must be of the type string, none returned at /srv/www/balloon/src/lib/Migration/Delta/CreateUniqueUserMailIndex.php:64)"} []
Describe the bug
The execution of "php /srv/www/balloon/src/cgi-bin/cli.php upgrade -vvv" ends with: [2019-09-10T13:24:03.741315+00:00] default.EMERGENCY: uncaught exception: Return value of Balloon\Migration\Delta\CreateUniqueUserMailIndex::createIndex() must be of the type string, none returned {"category":"Balloon\Bootstrap\Cli","exception":"[object] (TypeError(code: 0): Return value of Balloon\Migration\Delta\CreateUniqueUserMailIndex::createIndex() must be of the type string, none returned at /srv/www/balloon/src/lib/Migration/Delta/CreateUniqueUserMailIndex.php:64)"} []
To Reproduce
"docker exec -it balloon_balloon-dev_1 php /srv/www/balloon/src/cgi-bin/cli.php upgrade -vvv"
Expected behavior
[2019-09-10T12:54:58.283697+00:00] default.INFO: executed migration deltas successfully {"category":"Balloon\Migration"} []
Environment