def METHOD_NAME(self):
    """Tries to get a serial number from an APC device"""
    candidates = [k for k in self.nodes.keys() if 'IdentSerialNumber' in k]
    for c in candidates:
        serial = yield self.get_next(c)
        if serial:
            if isinstance(serial, bytes):
                serial = serial.decode("utf-8")
            defer.returnValue(serial)