Return a json dictionary representing this model.

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