这是我如何读取NFC标签信息：

func readerSession(_ session: NFCNDEFReaderSession, didDetect tags: [NFCNDEFTag]) {
    
    
    // Connect to the found tag and perform NDEF message reading
    let tag = tags.first!
    
    
    session.connect(to: tag, completionHandler: { (error: Error?) in
        
        tag.queryNDEFStatus(completionHandler: { (ndefStatus: NFCNDEFStatus, capacity: Int, error: Error?) in

            tag.readNDEF(completionHandler: { [self] (message: NFCNDEFMessage?, error: Error?) in
                
                for record in message!.records {
                    print("Type name: \(record.typeNameFormat)")
                    print("Payload size: \(record.payload)")
                    print("Type size: \(record.type)")
                    print("Identifier: \(record.identifier)")

                    print("Payload: " + String(data:record.payload, encoding: .utf8)!)
                    
                }
                
                
                session.invalidate()
            })
        })
    })
}

但标识符始终为0字节和空。我怎样才能读取一种唯一标识符或序列号？