AddPermission action needs extra validation for User Custom Field and Group Selector fields

If you go to the Add Permission page, choose a permission from the list on the left, choose Project Role on the right, but leave the selection as the default Choose a project role, the validation will correctly inform you that you need to select a value.

If the same is done for the User Custom Field or Group Selector options, it passes validation, and the permission selected is granted to Anyone. Instead, an error should be reported to the user.