iOS中的Twilio QuickStarter项目问题

Question

我已经下载了twilio quickstarter项目，并遵循docx并创建了聊天功能，并将URL传递到项目中的给定位置，现在当我运行该应用时，该应用因该错误而崩溃，Thread 10: EXC_BREAKPOINT (code=1, subcode=0x1048d85b0)。当尝试对请求中的数据进行序列化时，此错误会出现在他们的代码中。我如何摆脱这个问题？这是发生问题的代码，

struct TokenUtils {

static func retrieveToken(url: String, completion: @escaping (String?, String?, Error?) -> Void) {
    if let requestURL = URL(string: url) {

        let session = URLSession(configuration: URLSessionConfiguration.default)
        let task = session.dataTask(with: requestURL, completionHandler: { (data, response, error) in
            if let data = data {
                do {
                    let json = try JSONSerialization.jsonObject(with: data, options: []) as! [String:String]
                    let token = json["token"]
                    let identity = json["identity"]
                    completion(token, identity, error)
                }
                catch let error as NSError {
                    completion(nil, nil, error)
                }

            } else {
                completion(nil, nil, error)
            }
        })
        task.resume()
    }

}

}

这就是调试器中显示的内容， sort() method