Return a json dictionary representing this model.

def _to_dict(self):
        """Return a json dictionary representing this model."""
        _dict = {}
        if hasattr(self, 'feedback_id') and self.feedback_id is not None:
            _dict['feedback_id'] = self.feedback_id
        if hasattr(self, 'user_id') and self.user_id is not None:
            _dict['user_id'] = self.user_id
        if hasattr(self, 'comment') and self.comment is not None:
            _dict['comment'] = self.comment
        if hasattr(self, 'created') and self.created is not None:
            _dict['created'] = datetime_to_string(self.created)
        if hasattr(self, 'feedback_data') and self.feedback_data is not None:
            _dict['feedback_data'] = self.feedback_data._to_dict()
        return _dict