docs: def _to_dict(self):
          """Return a json dictionary representing this model."""
          _dict = {}
          if hasattr(self, 'classifier_id') and self.classifier_id is not None:
              _dict['classifier_id'] = self.classifier_id
          if hasattr(self, 'url') and self.url is not None:
              _dict['url'] = self.url
          if hasattr(self, 'text') and self.text is not None:
              _dict['text'] = self.text
          if hasattr(self, 'top_class') and self.top_class is not None:
              _dict['top_class'] = self.top_class
          if hasattr(self, 'classes') and self.classes is not None:
              _dict['classes'] = [x._to_dict() for x in self.classes]
          return _dict