title: Exception for Unhandle observer
body: <p>I am using following code to add observer:   </p>
  
  <pre><code>[self.priorityQueue addObserver:self forKeyPath:@"operations" options:options context:NULL];
  </code></pre>
  
  <p>And observe method is defined as:</p>
  
  <pre><code>-(void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object
                       change:(NSDictionary *)change context:(void *)context
  {
      if ([object isKindOfClass:[NSOperationQueue class]] &amp;&amp; [keyPath isEqualToString:@"operations"]) {
          //calling my method
      }
      else {       
          [super observeValueForKeyPath:keyPath ofObject:object
                        change:change context:context];
      }
  }
  </code></pre>
  
  <p>but I am getting following error:</p>
  
  <blockquote>
    <p>Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: ' (
     Context: 0x0, Property: 0x110bf60> ): An -observeValueForKeyPath:ofObject:change:context: message was received but not handled.
    Key path: operations
    Observed object: {name = 'NSOperationQueue 0x11213c0'}
    Change:</p>
  </blockquote>
  
  <p>Please tell me, if I am doing some mistake in my observer method.</p>
  
  <p>Thanks, </p>