title: How to fix "Object reference not set to an instance of object." when binding an event to an element generated by ListView ItemsSource when using MVVM?
body: <p>I have a ListView with an ItemsSource set to a kind of Movies collection (with Movie objects). And then inside I have a DataTemplate which contains a ComboBox and a TextBlock. 
  On the ComboBox I bind the Selected item to the progress (of episodes) that the Movie object contains. Here I'm using normal "Binding" method. But the problem arrives when I want to bind a method to the  "DropDownClosed" event. This works fine when using Code Behind, but using the ViewModel and x:Bind it gives me "Object reference not set to an instance of an object." when building my app.    </p>
  
  <p>The goal is to Bind to a method in the ViewModel, and not the Code Behind without the error.</p>
  
  <p>Everything works smooth when i take away the "DropDownClosed" event. And no other Events works any better.</p>
  
  <pre><code>&lt;ListView ItemsSource="{x:Bind ViewModel.MovieLibrary}"&gt;
      &lt;ListView.ItemTemplate&gt;
          &lt;DataTemplate&gt;
              &lt;StackPanel Spacing="20" Orientation="Horizontal"&gt;
                  &lt;ComboBox SelectedItem="{Binding Progress}"
                                            ItemsSource="{Binding Media.Episodes, Converter={StaticResource NumberToArrayConverter}}"
                                            DropDownClosed="{x:Bind ViewModel.UpdateStuff}"&gt;
                  &lt;/ComboBox&gt;
                  &lt;TextBlock Text="{Binding Media.Title}" TextWrapping="Wrap" /&gt;
              &lt;/StackPanel&gt;
          &lt;/DataTemplate&gt;
      &lt;/ListView.ItemTemplate&gt;
  &lt;/ListView&gt;
  </code></pre>
  
  <p>And this, but this works just as bad if it's empty so idk if this is necessary (from view model) :</p>
  
  <pre><code>public void UpdateStuff(object sender, object e)
          {
              //blabla not important
          }
  </code></pre>
  
  <p>The problem is I can't use x:Bind at all to any property.</p>