Alamofire: isSuccess 始终为真，即使有错误代码

服务器正在发送响应代码 404，但看起来框架正在将其解释为成功。

代码：

Alamofire.request(.GET, Constants.Path.rootUrl + "/api/users", parameters: ["username" : usernameString, "limit":3] , headers: ["tb-token" : userToken!])
            .responseJSON { response in


                print(response.request)  // original URL request
                print(response.response) // URL response
                print(response.data)     // server data
                print(response.result)   // result of response serialization


                let results = response.result

                if let JSON = response.result.value {

                    if response.result.isSuccess == true {
                        print("Success with JSON: \(JSON)")
                        self.tableView.hidden = false

                        self.resultsDict = results.value as! NSArray

                        let resultsNumber = results.value!.count

                        self.numberOfResults.text = "Results(\(resultsNumber))"
                        self.numberOfResults.hidden = false

                        self.resultsN = resultsNumber
                        self.loadedMode = true


                        self.tableView.reloadData()
                        self.tableView.hidden = false
                    }
                }
                    else {print("error")}

        }

isSuccess 始终为真，无论服务器发回什么代码。