title: extjs null data should load empty grid
body: <p>When the user select an item with info (json), the grid renders as expected.  </p>
  
  <p>But, when the returned data is null or {"total":0,"Products":null}, the grid keeps the previous selection.  </p>
  
  <p>The page is <a href="http://pssnet.com/~devone/dnc/dncEditProducts2.php" rel="nofollow noreferrer">here</a>: </p>
  
  <p>If the returned data is null, I need it to render it empty.  </p>
  
  <p>I am loading the grid as below:</p>
  
  <pre><code>    ProductsEditDataStore.baseParams.ProductTypeID =  ProductTypeID;
         ProductsEditDataStore.load({params:{start:0, limit:12}});
  </code></pre>