code: def set_value(self, model, value):
          
          if value is None and self.required:
              raise AttributeError("This field is required.")
  
          if value is not None:
              value = self._converter(value)
  
          setattr(model, self.storage_name, value)
docs: Set field's value.
  
          :param DomainModel model:
          :param object value: