Impossible to remove a group from myself.

[ghost]

Describe the issue
Problem done on a new and clean installation of Nameless.
When I remove a group, from myself, an error occurs and the group is not removed.

To Reproduce
Steps to reproduce the behaviour:

1. Go to the user manager and edit your profile.
2. Add any group to yourself and save.
3. Go back and edit your profile again.
4. Remove the previously added group and save.
5. See error.

Expected behaviour
The group should have been removed from the user.

Screenshots
https://user-images.githubusercontent.com/73427208/130448551-1ad13d6e-1406-420d-ac49-c1f2997bea5d.png
https://user-images.githubusercontent.com/73427208/130448563-d9122242-33b9-4b61-8d1d-492171bb3828.png

NamelessMC version (from StaffCP -> Overview)
NamelessMC 2.0.0-pr10

Additional information
I used Named Hosting, PHP 8.

[Derkades]

See #2296

It might be a PHP 8 issue, have you tried switching to PHP 7.4 in settings?