title: jQuery UI slider - Cannot call method 'addClass' of undefined
body: <p>I had this old jQuery UI slider that had worked just fine a few months ago, but now I seem to be getting an exception reading: Cannot call method 'addClass' of undefined. I've checked the values being passed into the slider and they're regular Javascript dates.</p>
  
  <pre><code>  $('#dateFilter').click(function() {
      return $('#sliderContainer').slideToggle(200);
    });
  
    $(function() {
      var endFiling, startFiling;
      startFiling = Date.parse($('#startFiling').val());
      endFiling = Date.parse($('#endFiling').val());
      return $('#filingDateSlider').slider({
        range: true,
        min: startFiling,
        max: endFiling,
        step: 86400000,
        values: [startFiling, endFiling],
        slide: function(event, ui) {
          var eD, end, sD, start;
          sD = new Date(ui.values[0]);
          start = dateFormat(sD);
          eD = new Date(ui.values[1]);
          end = dateFormat(eD);
          $('#filingStartDate').text(start);
          return $('#filingEndDate').text(end);
        }
          });
  </code></pre>
  
  <p>Is there a particular reason why I might be getting this new error?</p>
  
  <p><a href="https://i.imgur.com/xC2E6.jpg" rel="noreferrer">http://i.imgur.com/xC2E6.jpg</a></p>