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