def _rpad(self, length, pad=' '):
    return _ops.RPad(self, length, pad).to_expr()
This uses self.mongo, which uses config without document_class
dataset/ETHPy150Open cloudera/ibis/ibis/expr/api.py/_rpad--crossover with--dataset/ETHPy150Open dcrosta/flask-pymongo/tests/test_config.py/CustomDocumentClassTest.test_create_without_document_class