Using Ceeram suggestions with a workaround exposing getMissingFields

kimsia: else store missing fields in a behavior attribute, and create a
method to retrive them?
[19:11] <kimsia> Ceeram: okay got it. i go try
[19:13] <Ceeram> kimsia: you cant do it indeed, as behavior methods are
called with call_user_func_array, which cant pass by reference