title: PresentationSource.FromVisual(this) returns null value in WPF
body: <p>I'm using the following code for my:</p>
  
  <pre><code>protected override void OnSourceInitialized(EventArgs e)
  {
  ...
  ....
  HwndSource source = PresentationSource.FromVisual(this) as HwndSource;
  ...
  ...
  }
  </code></pre>
  
  <p>In some systems the "source" value comes out to be null and i cant find the reason why...</p>