title: Extra argument 'error' in call - Unable to build my Xcode project
body: <pre><code>import Foundation
  
  class NetworkOperation {
  
      lazy var config: NSURLSessionConfiguration =     NSURLSessionConfiguration.defaultSessionConfiguration()
      lazy var session: NSURLSession = NSURLSession(configuration: self.config)
      let queryURL: NSURL
  
      typealias JSONDictionaryCompletion = ([String: AnyObject]? -&gt; Void)
  
      init(url: NSURL) {
          self.queryURL = url
      }
  
      func downloadJSONFromURL(completion: JSONDictionaryCompletion) {
  
          let request = NSURLRequest(URL: queryURL)
          let dataTask = session.dataTaskWithRequest(request) {
              (let data, let response, let error) in
  </code></pre>
  
  <p><em>// 1. Check HTTP response for successful GET request</em>  </p>
  
  <pre><code>            if let httpResponse = response as? NSHTTPURLResponse {
                  switch httpResponse.statusCode {
                  case 200:
  </code></pre>
  
  <p><em>// 2. Create JSON object with data</em>  </p>
  
  <pre><code>                    let jsonDictionary = NSJSONSerialization.JSONObjectWithData(data, options: nil, error: nil)
                      completion(jsonDictionary)
                  default:
                      print("GET request not successful. HTTP status code: \(httpResponse.statusCode)")
                  }
              } else {
                  print("Error: Not a valid HTTP response")
              }
          }
  
          dataTask.resume()
      }
  }
  </code></pre>
  
  <p><em>In the 'Create JSON object with data' step, I keep receiving the "extra argument 'error' in call". What is happening? I am unable to find documentation to help me further in this.</em></p>