Return a json dictionary representing this model.

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