code: def get_view_model(cls):
      
      msg = 'When using get_queryset you must set a auto_filters_model field in the viewset'
      if cls.queryset is not None:
          return cls.queryset.model
      else:
          assert hasattr(cls, 'auto_filters_model'), msg
          return cls.auto_filters_model
docs: Get the model to use in the filter_class by inspecting
      the queryset or by using a declared auto_filters_model