title: Core Data doesn't store nil over app restart
body: <p>I have 2 objects in Core Data; </p>
  
  <p>CurrentSession, Session</p>
  
  <p>currentSession.session has 1 session, aka; </p>
  
  <pre><code>currentSession.session = session; 
  [self save]; // which does the context save 
  </code></pre>
  
  <p>This all works very well, however, when I do ; </p>
  
  <pre><code>currentSession.session = nil; 
  [self save]; 
  </code></pre>
  
  <p>it works well as long as i'm in the running application I did that in. When I restart the application from Xcode and come back in it, currentSession.session suddenly is not nil anymore. It's the value it was before I set it to nil. </p>
  
  <p>I tried running     </p>
  
  <p>[[self dataContext] processPendingChanges]; </p>
  
  <p>the changes as well with the result. What could be the issue here? </p>