title: jQuery datatable moment date format sorting plugin is not working for if I added "NA" or "---" as empty date value
body: <p>I used jQuery Datatable and the momentjs date format plugin of data table for date sorting in my application. Data table sorting is implemented for client site (sorting should happen in the DOM, not on request to the server and load data).
  So, if I set an empty string as the value for one of the Data table <code>td</code> elements from date column, then it works fine, but when I set the value to 'NA' or '---' instead of an empty value then the sorting is not working properly.</p>
  
  <pre><code>Check code on jsfiddle 
  </code></pre>
  
  <blockquote>
    <p><a href="https://jsfiddle.net/ranjit_redekar/b0p3qLtg/16/" rel="nofollow noreferrer">https://jsfiddle.net/ranjit_redekar/b0p3qLtg/16/</a></p>
  </blockquote>
  
  <p><strong>Not working when I use Any string (e.g '---')</strong></p>
  
  <p><a href="https://i.stack.imgur.com/pZkyc.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/pZkyc.png" alt="Not working example"></a></p>
  
  <p><strong>Sorting works when I use empty string</strong>
  <a href="https://i.stack.imgur.com/2Gthe.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/2Gthe.png" alt="Working Example"></a></p>