title: Don't render Image when Image.Source is empty
body: <p>In the ListView, I need to show some images and text, only display the text when the <code>Image.Source</code> is empty. How to do?</p>
  
  <pre><code>&lt;ListView ItemsSource="{x:Bind ViewModel.News}"&gt;
      &lt;ListView.ItemTemplate&gt;
          &lt;DataTemplate x:DataType="home:NormalNews"&gt;
              &lt;StackPanel&gt;
                  &lt;TextBlock Text="{x:Bind Title}"/&gt;
                  &lt;Image Source="{x:Bind Thumbnail}"/&gt;
              &lt;/StackPanel&gt;
          &lt;/DataTemplate&gt;
      &lt;/ListView.ItemTemplate&gt;
  &lt;/ListView&gt;
  </code></pre>
  
  <p>ViewModel Data Source like:</p>
  
  <pre><code>News.Add(new NormalNews{ Title = "title1", Thumbnail = "http://a.com/test.jpg" });
  News.Add(new NormalNews{ Title = "title2", Thumbnail = "" });
  </code></pre>
  
  <p>When I tried to run  this page, it stopped running.</p>