def _to_dict(self):
        """Return a json dictionary representing this model."""
        _dict = {}
        if hasattr(self, 'classifier_id') and self.classifier_id is not None:
            _dict['classifier_id'] = self.classifier_id
        if hasattr(self, 'name') and self.name is not None:
            _dict['name'] = self.name
        if hasattr(self, 'owner') and self.owner is not None:
            _dict['owner'] = self.owner
        if hasattr(self, 'status') and self.status is not None:
            _dict['status'] = self.status
        if hasattr(self,
                   'core_ml_enabled') and self.core_ml_enabled is not None:
            _dict['core_ml_enabled'] = self.core_ml_enabled
        if hasattr(self, 'explanation') and self.explanation is not None:
            _dict['explanation'] = self.explanation
        if hasattr(self, 'created') and self.created is not None:
            _dict['created'] = datetime_to_string(self.created)
        if hasattr(self, 'classes') and self.classes is not None:
            _dict['classes'] = [x._to_dict() for x in self.classes]
        if hasattr(self, 'retrained') and self.retrained is not None:
            _dict['retrained'] = datetime_to_string(self.retrained)
        if hasattr(self, 'updated') and self.updated is not None:
            _dict['updated'] = datetime_to_string(self.updated)
        return _dict
Return a json dictionary representing this model.