title: Mongo {$ne : null} not working as expected
body: <p>When I issue the following query:</p>
  
  <pre><code>db.users.find({"pic.status" : {$ne : null} }, {"pic" : 1}).toArray()
  </code></pre>
  
  <p>I expect to receive all users whose pic.status is NOT null. However, the actual result looks something like this:</p>
  
  <pre><code>{                                                                                                                                      
      "_id" : ObjectId("4f1e1ab9cdf9dbaa160000bf"),
      "pic" : {
          "id" : "4f1e1ab9cdf9dbaa160000be",                                                                                                                                                                                                                                                                                                                      
          "status" : null
      }
  },
  {
      "_id" : ObjectId("4f1e28480eaf38193d00006f"),
      "pic" : {
          "id" : "4f1e28480eaf38193d00006e",                                                                                                                                                                                                                                                                                                                      
          "status" : null
      }
  }
  </code></pre>
  
  <p>That is, I receive users whose pic.status IS null. How can I fix this?</p>