fix(team): Add nullable team_id

[Androlax2]

Added null to helpers getPermissionsTeamId and setPermissionsTeamId and in the PermissionRegistrar.

This is to fix a PHPStan problem :

Parameter #1 $id of function setPermissionsTeamId expects Illuminate\Database\Eloquent\Model|int|string, null given.

But when you put '', my tests are failing because it expects a null as per the doc.