title: Get back value of Object key'ed NSMutableDictionary
body: <p>I have a case where I need to have <code>NSMutableDictionary</code> with <code>NSManagedObject</code> as the key.</p>
  
  <p>Based on this <a href="https://stackoverflow.com/questions/1497622/nsmanagedobject-as-nsdictionary-key">post</a>, I can set <code>NSManagedObject</code> as key in dictionary by:
  <code>[NSValue valueWithNonretainedObject:]</code></p>
  
  <pre><code>NSMutableDictionary *dict = [[NSMutableDictionary alloc] init];
  [dict setObject:product forKey:[NSValue valueWithNonretainedObject:category]];
  </code></pre>
  
  <p>How can I get back the value of dict? I've tried using NSValue again but it crash with no description.</p>