title: NSRangeException error - In-App-Purchase implemantaition
body: <p>I've implemented an In-App-Purchase into my app. 
  If I run my app and press the "purchase" button, i get the following error:</p>
  
  <pre><code>2014-10-22 17:48:20.733 MyApp[170:3435] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayI objectAtIndex:]: index 0 beyond bounds for empty array'
  </code></pre>
  
  <p>Does someone got the same error and know what's to do?</p>