docs: def _to_dict(self):
          """Return a json dictionary representing this model."""
          _dict = {}
          if hasattr(self, 'available') and self.available is not None:
              _dict['available'] = self.available
          if hasattr(self,
                     'maximum_allowed') and self.maximum_allowed is not None:
              _dict['maximum_allowed'] = self.maximum_allowed
          return _dict