title: In WPF, is the FallbackValue used when the binding fails due to null references?
body: <p>My view-model exposes a list called <code>MyList</code> that may be empty or <code>null</code>. I have an element that I would like hide based on this state. If <code>MyList</code> is empty or <code>null</code>, then the element should be collapsed. If it has elements then it should be shown. </p>
  
  <p>Here is my <code>DataTrigger</code>: </p>
  
  <pre><code>&lt;DataTrigger Binding="{Binding MyList.Count, FallbackValue=0}" Value="0"&gt;
      &lt;Setter Property="Visibility" Value="Collapsed"&gt;&lt;/Setter&gt;
  &lt;/DataTrigger&gt;
  </code></pre>
  
  <ul>
  <li>What happens to this <code>DataTrigger</code> when <code>MyList</code> is <code>null</code>? </li>
  <li>Will it use the <code>FallbackValue</code> or will it fail? </li>
  <li>Is this documented somewhere? </li>
  </ul>