I had a PHP Notice:
PHP Notice: Trying to access array offset on value of type bool in Filechecks.php:205
while the actual problem was, that I was inside a docker container and had the wrong group-id assigned.
I only had a notice, since the user permissions still worked, but I think that place needs better handling. This PR is a first try to improve the situation.
I merged this, @aragon999, thanks again for the contribution!