title: UILocalNotification userInfo not serializing NSURL
body: <p>I am trying to do</p>
  
  <pre><code>UILocalNotification *notification = [[UILocalNotification alloc] init];
  NSURL *urlForSomeObject=[[(NSManagedObject *)someObject objectID] URIRepresentation];
  notification.fireDate  = aDate;
  notification.timeZone  = [NSTimeZone systemTimeZone];
  notification.soundName = UILocalNotificationDefaultSoundName;
  notification.applicationIconBadgeNumber = 1;
  notification.userInfo=[NSDictionary  dictionaryWithObject:urlForSomeObject            forKey:@"objectUrl"];
  </code></pre>
  
  <p>when notification occurs app gives the exception 
  <code>unable to serialize userInfo: (null)'</code> 
  I have checked that [NSDictionary  dictionaryWithObject:urlForSomeObject            forKey:@"objectUrl"] returns a valid dictionary.
  why is this behavior occurring. As far i knw NSURL adhere to NSCoding protocol and should be serialized. 
  can somebody help me out?</p>