title: NavigationService.navigate null reference exception
body: <p>I'm learning WP coding and I have problem that I can't solve :/</p>
  
  <pre><code>try
   {
      NavigationService.Navigate(new Uri("/edit.xaml", UriKind.Relative));
   }
   catch (Exception ex)
   {
       MessageBox.Show(ex.Message.ToString(),"Error!",MessageBoxButton.OK);
   }
  </code></pre>
  
  <p>edit.xaml is in the same directory as MainPage.xaml</p>
  
  <p>It throws "NullReferenceException"</p>