docs: def add_to_results(self, data, label, results):
          """
          responsible for updating the running `results` variable with the
          data from this queryset/serializer combo
          """
          raise NotImplementedError(
              '{} must specify how to add data to the running results tally '
              'by overriding the `add_to_results` method.'.format(
                  self.__class__.__name__
              )
          )