I am getting nil Optional(Stormy.DarkSkyError.invalidUrl)

// base url to interact with the DkSky api used to make each call when we need it in future
lazy var baseUrl: URL = {

    //paste "base" from VC.
    //let base = The Darksky connection URL but mmodified as below
    //chg "let base=" to  "return" and "darksky" to "self.apiKey"
    //now we have an optional Url but we force unwrap with !
    return URL(string: "https://api.darksky.net/forecast/\(self.apiKey)/")! // its cool to  crash with ! if url cant be created.
}()

let downloader = JSONDownloader() // hold on to an  instance of JSONDownloader()

typealias CurrentWeatherCompletionHandler = (CurrentWeather?, DarkSkyError?)-> Void

func getCurrentWeather(at coordinate: Coordinate, completionHandler completion: @escaping CurrentWeatherCompletionHandler) {


    guard let url = URL(string: coordinate.description, relativeTo: baseUrl) else {// make url
        completion(nil, .invalidUrl)// make this error in DarkSkyError file
        return
    }

    let request = URLRequest(url: url)//make a requestor to use to make requests with

    // ask JSONDownloader to make a request on our behalf
    let task = downloader.jsonTask(with: request) { json, error in

        // after we create the Current Weather instance and convert it to Json in the CurrentWeather file
        guard let json = json else{// unwrap the task
            completion(nil, error)
            return
        }// now we have a valid json object

        guard let currentWeatherJson = json["currently"] as? [String: AnyObject], let currentWeather = CurrentWeather(json: currentWeatherJson) else {
            completion(nil, .jsonParsingFailure)
            return
        }

        completion(currentWeather,nil)

        // now the taks is made and ready
    }

    task.resume() // this will actually start the task
}