Error when saving after removing all groups from a user

[Derkades]

in_array(): Argument #2 ($haystack) must be of type array, null given
(File: /data/modules/Core/pages/panel/users_edit.php)

/data/modules/Core/pages/panel/users_edit.php line 245

/panel/users/edit/?id=1

[Derkades]

Only happens with admin users, normal users give a "You must select a user's group" error when trying to save with no groups selected. For the admin user, the primary group is not included in the secondary group selection box while for normal users it is.

[samerton]

Duplicate of #2335