bool Item_field::switch_to_nullable_fields_processor(void *arg)
{
  Field **new_fields= (Field **)arg;
  set_field_to_new_field(&field, new_fields);
  set_field_to_new_field(&result_field, new_fields);
  maybe_null= field && field->maybe_null();
  return 0;
}
bool Item_field::switch_to_nullable_fields_processor(void *arg)
{
  Field **new_fields= (Field **)arg;
  set_field_to_new_field(&field, new_fields);
  set_field_to_new_field(&result_field, new_fields);
  maybe_null= field && field->maybe_null();
  return 0;
}