Return a json dictionary representing this model.

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