title: why the data object of datataskwithurl is receiveing null?
body: <p>I want to fetch some data from my backend to my app. I wrote following code:</p>
  
  <pre><code>NSURL *url = [NSURL URLWithString:@"http://domain.com/books"];
      config = [NSURLSessionConfiguration defaultSessionConfiguration];
      //curl -H 'Authorization: Token token="replace-with-token"'
      [config setHTTPAdditionalHeaders:@{@"Authorization":@"Token token=\"7601ea35c7eaf067fefe\""}];
      NSURLSession *session = [NSURLSession sessionWithConfiguration:config];
      [[session dataTaskWithURL:url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
          NSError *error1=nil;
          NSArray *JSON=[NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:&amp;error1];
      }
  
        ] resume];
  </code></pre>
  
  <p>I check the response object and I got 200,seems the fetch request went well. but I got the null as for requested data. I think sth from parsing data went wrong. here is it is an example of what I expected to recieve.I aslo put the example out put into JSON viewer <a href="http://jsonviewer.stack.hu" rel="nofollow">http://jsonviewer.stack.hu</a> . it shows sth like {} at the first side, but when I open it, it shows data correctly.</p>
  
  <pre><code>[
       {
          "id": 437,
          "name": "alchemist",
          "description": "story book.",
          "favorite": false,
          "difficulty": 3,
          "created_at": "2014-09-29T10:43:00.072Z",
          "updated_at": "2014-11-26T11:53:58.451Z",
          "photo": {
            "url": "https://amazon-/uploads/books/photo/437/alchemist.jpg",
            "thumbnail_url": "https://amazon-books.amazonaws.com/uploads/recipe/photo/437/alchemist-PC.jpg"
          }
        }
      ]
  </code></pre>
  
  <p>Does any one know the reason?
  This is an update for my question, here it is the nsurlresponse object:</p>
  
  <pre><code>{ status code: 200, headers {
      "Cache-Control" = "max-age=0, private, must-revalidate";
      Connection = "keep-alive";
      "Content-Length" = 2;
      "Content-Type" = "application/json; charset=utf-8";
      Date = "Sat, 11 Jul 2015 15:26:58 GMT";
      Etag = "\"d751713988987e9331980363e24189ce\"";
      Server = "WEBrick/1.3.1 (Ruby/2.0.0/2015-04-13)";
      Via = "1.1 vegur";
      "X-Content-Type-Options" = nosniff;
      "X-Frame-Options" = SAMEORIGIN;
      "X-Request-Id" = "8e1abb2e-2526-4d10-99e7-d553b51457fd";
      "X-Runtime" = "0.125302";
      "X-Ua-Compatible" = "chrome=1";
      "X-Xss-Protection" = "1; mode=block";
  } }
  </code></pre>