Return a json dictionary representing this model.

def _to_dict(self):
        """Return a json dictionary representing this model."""
        _dict = {}
        if hasattr(self, 'feedback_type') and self.feedback_type is not None:
            _dict['feedback_type'] = self.feedback_type
        if hasattr(self, 'document') and self.document is not None:
            _dict['document'] = self.document._to_dict()
        if hasattr(self, 'model_id') and self.model_id is not None:
            _dict['model_id'] = self.model_id
        if hasattr(self, 'model_version') and self.model_version is not None:
            _dict['model_version'] = self.model_version
        if hasattr(self, 'location') and self.location is not None:
            _dict['location'] = self.location._to_dict()
        if hasattr(self, 'text') and self.text is not None:
            _dict['text'] = self.text
        if hasattr(self,
                   'original_labels') and self.original_labels is not None:
            _dict['original_labels'] = self.original_labels._to_dict()
        if hasattr(self, 'updated_labels') and self.updated_labels is not None:
            _dict['updated_labels'] = self.updated_labels._to_dict()
        if hasattr(self, 'pagination') and self.pagination is not None:
            _dict['pagination'] = self.pagination._to_dict()
        return _dict