         } else {
             let userInfo = [NSLocalizedDescriptionKey: "failed to build request."]
             let error = NSError(domain: APIKitErrorDomain, code: 0, userInfo: userInfo)
-            dispatch_async(mainQueue, { handler(.failure(error)) })
+            dispatch_async(mainQueue) { handler(.failure(error)) }
 
             return nil
         }

            task.request = Box(request)
            task.completionHandler = { data, URLResponse, connectionError in
                if let error = connectionError {
                    dispatch_async(mainQueue, { handler(.failure(error)) })
                    return
                }
                

                    }
                }

                dispatch_async(mainQueue) { handler(mappedResponse) }
            }
            
            task.resume()
