Return a json dictionary representing this model.

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