title: Attempting to get auto layout values with nil engine
body: <p>I'm using auto layout in my project and I get the following message in the console window:</p>
  
  <p><code>Attempting to get auto layout values with nil engine. Affected view:</code></p>
  
  <p>This happens if I try to update my view hierarchy in <code>observeValueForKeyPath:ofObject:change:context:</code></p>
  
  <p>Does anyone know what the reason for this behavior can be?</p>