swift3.0中的Json解析

这是我在Swift中解析Jason的代码：

 static func POST(url: String, parameters: NSDictionary, completionBlock: @escaping CompletionBlock){

        let todoEndpoint: String = Webservices.Base_Url.appending(url)

        guard let url = NSURL(string: todoEndpoint) else {
            print("Error: cannot create URL")
            return
        }
         var request = URLRequest(url: url as URL)

        //var request = URLRequest(url: NSURL(string: todosEndpoint)! as URL)
        let session = URLSession.shared
        request.httpMethod = "POST"

        var err: NSError?
        let jsonData = try? JSONSerialization.data(withJSONObject: parameters)

        request.httpBody = jsonData
        request.addValue("application/x-www-form-urlencoded;charset=UTF-8 ", forHTTPHeaderField: "Content-Type")
        request.addValue("application/json", forHTTPHeaderField: "Accept")

        let task = session.dataTask(with: request, completionHandler: {data, response, error -> Void in
            guard error == nil else {
                                print("error calling POST on /todos/1")
                                print(error)
                                return
                            }


            // make sure we got data
            guard let dataTemp = data else {
                print("Error: did not receive data")
                return
            }

            // parse the result as JSON, since that's what the API provides
            do {
                      guard let todo = try JSONSerialization.jsonObject(with: dataTemp, options: []) as? [String: AnyObject] else {
                        print("error trying to convert data to JSON")
                        return
                }

                // now we have the todo, let's just print it to prove we can access it
                print("The todo is: " , todo)

                // the todo object is a dictionary
                // so we just access the title using the "title" key
                // so check for a title and print it if we have one

            } catch  {
                print("error trying to convert data to JSON")
                return
            }


                        })

        task.resume()

}

我在分析jason时得到：

错误表达式生成错误：错误：执行被中断， 原因：EXC\u访问错误（代码=1，地址=0x0）。这一过程已经完成 返回到表达式计算前的状态

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出什么问题了？

您能识别出它崩溃的线路吗？最有可能的是jsonData为零