Return a json dictionary representing this model.

def _to_dict(self):
        """Return a json dictionary representing this model."""
        _dict = {}
        if hasattr(self, 'entities') and self.entities is not None:
            _dict['entities'] = [x._to_dict() for x in self.entities]
        if hasattr(self, 'location') and self.location is not None:
            _dict['location'] = self.location
        if hasattr(self, 'text') and self.text is not None:
            _dict['text'] = self.text
        return _dict