title: Nested JSON data will cause crash using NS Dictionary (in Swift)
body: <p>I'm trying to fetch movie information in JSON format using JSONSerialization in Swift and save it as an NSDictionary. However, calling the Rotten Tomatoes API (in which information is nested) will cause my Playground to crash (without giving me any useful errors). </p>
  
  <p>I know the code is somewhat valid, since calling other APIs which don't nest their data works (but don't fulfill my need).</p>
  
  <p>Here's the code:</p>
  
  <pre><code>func getJSON(urlToRequest: String) -&gt; NSDictionary {
      var url = NSURL(string: urlToRequest)
  
      var error: NSError?
      let jsonData: NSData = NSData.dataWithContentsOfURL(url , options: NSDataReadingOptions.DataReadingMapped, error: nil)
  
      let jsonDict = NSJSONSerialization.JSONObjectWithData(jsonData, options: NSJSONReadingOptions.MutableContainers, error: &amp;error) as NSDictionary
  
      return jsonDict
  }
  let movieData: NSDictionary = getJSON(apiURL)
  </code></pre>
  
  <p>here's a sample from the Rotten Tomatoes API JSON (shortened for illustration purposes, this is the actual JSON file, not the output from my code)</p>
  
  <pre><code>{
      "id": 770672122,
      "title": "Toy Story 3",
      "year": 2010,
      "genres": ["Animation", "Kids &amp; Family", "Science Fiction &amp; Fantasy", "Comedy"],
      "release_dates": {
          "theater": "2010-06-18",
          "dvd": "2010-11-02"
      },
      "ratings": {
          "critics_rating": "Certified Fresh",
          "critics_score": 99,
          "audience_rating": "Upright",
          "audience_score": 89
      }
  }
  </code></pre>