title: datatables yadcf custom function not triggered
body: <p>I'm using datatables and the yadcf plugin which is working well. However I'm trying to add a custom filter and having no luck getting it to work. It appears it is being ignored.</p>
  
  <p>Basically I want to filter whether a cell is empty or has data</p>
  
  <p>I used this example as a starting point:
  <a href="http://yadcf-showcase.appspot.com/DOM_source.html" rel="nofollow">http://yadcf-showcase.appspot.com/DOM_source.html</a></p>
  
  <p>My custom function is:</p>
  
  <pre><code>function filterGroupName(filterVal, columnVal) {
      var found;
      if (columnVal === '') {
          return true;
      }
      switch (filterVal) {
          case 'Groups':
              found = columnVal.length &gt; 0;
              break;
          case 'No Groups':
              found = columnVal.length &lt; 1 || columnVal === '';
              break;
          default:
              found = 1;
              break;
      }
  
      if (found !== -1) {
          return true;
      }
      return false;
  }
  </code></pre>
  
  <p>And here is the part of the script that sets up yadcf:</p>
  
  <pre><code>{
      column_number: 3,
      filter_container_id: "filter-group-name",
      filter_type: "custom_func",
      data: [{
          value: 'Groups',
          label: 'Groups'
      }, {
          value: 'No Groups',
          label: 'No Groups'
      }],
      filter_default_label: "Select  Groups",
      custom_func: filterGroupName
  
  }
  </code></pre>
  
  <p>I've set a breakpoint in the script to see what's happening but it never gets triggered</p>
  
  <p>The page gets the correct select boxes created but selecting either option returns no entries - everything is being filtered out in the datatable.</p>
  
  <p>So, what have I missed in getting the function to work?</p>
  
  <p>Thank you</p>