docs: def to_representation(self, value):
          """
          Transform the *outgoing* native value into primitive data.
          """
          raise NotImplementedError(
              '{cls}.to_representation() must be implemented for field '
              '{field_name}. If you do not need to support write operations '
              'you probably want to subclass `ReadOnlyField` instead.'.format(
                  cls=self.__class__.__name__,
                  field_name=self.field_name,
              )
          )