docs: def get_formset_class(self, **kwargs):
          """
          Returns the formset for the queryset,
          if a form class is available.
          """
          form_class = self.get_formset_form_class()
          if form_class:
              kwargs['formfield_callback'] = self.formfield_for_dbfield
              return model_forms.modelformset_factory(self.model,
                          form_class, fields=self.change_fields, extra=0,
                          **kwargs)