title: WPF display message instead of menu items in menu when bound menus list is empty
body: <p>I have a menu that looks something like this:</p>
  
  <pre><code>&lt;MenuItem x:Name="menu" ItemsSource="{Binding Items}" Style="{StaticResource ItemStyle}"&gt;
      &lt;MenuItem.Header&gt;
          ...
      &lt;/MenuItem.Header&gt;
      &lt;MenuItem.ItemContainerStyle&gt;
          &lt;Style TargetType="{x:Type MenuItem}"&gt;
              &lt;Setter Property="PropertyNameOne" Value="{Binding}"/&gt;
              &lt;Setter Property="PropertyNameTwo" Value="{Binding}"/&gt;
          &lt;/Style&gt;
      &lt;/MenuItem.ItemContainerStyle&gt;
  &lt;/MenuItem&gt;
  </code></pre>
  
  <p><code>Items</code> is a <code>NotifyingCollection</code>. However, when the <code>Items</code> list is empty, I would like to display a message, like "No items in menu.", instead of the current behavior, which is a tiny little empty box. Is there a way to do this just in XAML?</p>