Unresolved identifier error for Swift course Weather App

 override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        let baseURL = NSURL(string: "https://api.forecast.io/forecast/\(apiKey)/")
        let forecastURL = NSURL(string: "43.025938, -88.029553", relativeToURL: baseURL)

        let sharedSession = NSURLSession.sharedSession()
        let downloadTask: NSURLSessionDownloadTask = sharedSession.downloadTaskWithURL(forecastURL, completionHandler: { (location: NSURL!, response: NSURLResponse!, error: NSError!) -> Void in
        })

// ---------> I'm Receiving the error on the line below

         if (error == nil) {
            let dataObject = NSData(contentsOfURL: location)
            let weatherDictionary: NSDictionary = NSJSONSerialization.JSONObjectWithData(dataObject, options: nil, error: nil) as
            NSDictionary

            let currentWeather = Current(weatherDictionary: weatherDictionary)
            println(currentWeather.tempature)
        }

    }