title: undefined value working in jquery 1.8.3 but not in 1.9.1
body: <p>in 1.8.3 my flow goes in to this if condition but not in 1.9.1 </p>
  
  <pre><code>    var order_node = $('div.oe_website_sale_tx_status');  
      if (! order_node || order_node.data('orderId') === undefined) {
          return;
      }
  </code></pre>
  
  <p>if <code>.data()</code> is changed in new version.</p>
  
  <p><strong>HTML</strong></p>
  
  <pre><code>&lt;div class="oe_website_sale_tx_status" data-order-id="order.id"&gt;
   .....
   .....
  &lt;/div&gt;
  </code></pre>