title: Yii2: How to put null values to the end of an object list when sorting is ascending?
body: <p>Here is my DataProvider:</p>
  
  <pre><code>$dataProvider = new ActiveDataProvider([
      'query'      =&gt; $query,
      'pagination' =&gt; ['pageSize' =&gt; 50],
      'sort'       =&gt; [
          'defaultOrder' =&gt; [
              'priority'      =&gt; SORT_DESC,
              'date_targeted' =&gt; SORT_ASC
          ]
       ]
  ]);
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/KJg5D.png" alt="enter image description here"></p>
  
  <p><img src="https://i.stack.imgur.com/xrmW0.png" alt="enter image description here">
  <img src="https://i.stack.imgur.com/Hd5tX.png" alt="enter image description here">
  What I want is to move ("not set") to the end of the results.</p>
  
  <p>How can I do this?</p>