private Object handleForm(Object tos) {
      if (tos instanceof GedcomVersion && ((GedcomVersion)tos).getForm() == null) {
         return new FieldRef(tos, "Form");
      }
      else if (tos instanceof Media && ((Media)tos).getFormat() == null) {
         return new FieldRef(tos, "Format");
      }
      return null;
   }