title: MongoDB queries with null value
body: <p>My collection (MongoDB v 2.0.2) has following records:</p>
  
  <pre><code>db.organization.find({})
  { "_id" : 1001, "path" : [ ], "parent" : null }
  { "_id" : 1002, "path" : [ 1001 ], "parent" : NumberLong(1001) }
  </code></pre>
  
  <p><code>organization</code> has indexes:</p>
  
  <pre><code>db.organization.ensureIndex({"path":1});
  db.organization.ensureIndex({"parent":1},{sparse:false});
  </code></pre>
  
  <p>(note I put awarnes <code>sparse : false</code> - to grant that null is indexed)
  But, executing:</p>
  
  <pre><code>db.organization.find({"parent":null})
  </code></pre>
  
  <p>Returns empty set. What is wrong? Thank you in advance</p>