How to use the pybatfish.question.bfq.undefinedReferences function in pybatfish

def test_config_sanity(isFailed):
    logging.info("Progress: Searching for unused and undefined data structures")
    # Find all undefined data structures
    undefined = bfq.undefinedReferences().answer().frame()
    if len(undefined) >  0:
        logging.error("Found undefined data structures")
        logging.error(undefined)
        isFailed = True
    else:
        logging.info("No undefined data structures found")

    # Find all unused data structures
    unused = bfq.unusedStructures().answer().frame()
    if len(unused) >  0:
        logging.error("Found unused data structures")
        logging.error(unused)
        isFailed = True
    else:
        logging.info("No unused data structures found")