title: Query where not equal to null or empty
body: <p>I am trying to find all the documents where email exists.</p>
  
  <p>I am trying the following find query:</p>
  
  <pre><code>{ "email": {$exists:true, $ne:null, $ne:""}}
  </code></pre>
  
  <p>Still I am getting documents where email is <code>null</code>. </p>
  
  <p>Can anyone tell me what I am doing wrong?</p>