title: Parse iOS SDK: strange "cannot do a comparison query of type: (NULL)"
body: <p><strong>Scenario</strong></p>
  
  <p>I have been using the parse.com framework for over 6 months now on a project. It seems like it is very glitchy and full of bugs but this is something that I need to know if I'm doing it the right way. I am trying to use a PFQueryTableViewController to display similar user's info to a user. I use the code...</p>
  
  <pre><code>-(PFQuery *)queryForTable {
  
      PFQuery *matchQuery = [PFUser query];
      [matchQuery whereKey:@"mostCommon" equalTo:[PFUser currentUser][@"mostCommon"]];
      [matchQuery whereKey:@"userID" notEqualTo:currentUserID];
      return matchQuery;
  
  }
  </code></pre>
  
  <p><strong>Problem</strong></p>
  
  <p>When I run this and try to push this PFQTVC onto the stack, I get this error message...</p>
  
  <pre><code>*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Cannot do a comparison query for type: (null)'
  </code></pre>
  
  <p>This is usually to do with not having your information set in the database. I am providing the image below to illustrate there <strong>IS</strong> indeed data in the data browser. </p>
  
  <p><img src="https://i.stack.imgur.com/ZdA3D.png" alt="enter image description here"></p>
  
  <p><strong>Question</strong></p>
  
  <p>So if the query is correct, and the data is there... <strong>THEN WHY IS THE APP CRASHING</strong>?</p>