title: Combobox contains an empty item
body: <p>I've got a combobox</p>
  
  <pre><code>&lt;ComboBox ItemsSource="{Binding MyItems}" 
            DisplayMemberPath="DisplayedName" 
            SelectedValue="{Binding MySelectedItem}"/&gt;
  </code></pre>
  
  <p>and strangely, there is a blank, empty item at the last position when I open the combobox. Why is that? The last, empty entry is also selectable. The collection I am binding to does not contain an empty entry. It contains e.g. 4 items, but the combobox has 5.</p>
  
  <p><strong>EDIT:</strong></p>
  
  <p>The property in my ViewModel:</p>
  
  <pre><code>public ObservableCollection&lt;MyItem&gt; MyItems { get; set; }
  private MyItem mySelectedItem { get; set; }
  public MyItem MySelectedItem {
      get { return mySelectedItem }
      set { 
               mySelectedItem = value;
               RaisePropertyChanged(() =&gt; MySelectedItem);
           }
  }
  </code></pre>
  
  <p>I'm setting <code>MyItems</code> to a collection of available items:</p>
  
  <pre><code>MyItems = AvailableItems();
  ...
  public ObservableCollection&lt;MyItem&gt; AvailableItems()
  {
      return new ObservableCollection&lt;MyItem&gt;()
      {
          new MyItem() {DisplayedName = "ItemNameIMadeUp1"},
          new MyItem() {DisplayedName = "ItemNameIMadeUp2"}
      };
  }
  </code></pre>
  
  <p>And I am defining a certain item as selected item:</p>
  
  <pre><code>MySelectedItem = MyItems[0];
  </code></pre>
  
  <p><strong>EDIT2</strong>
  I've found out that the "empty" item is a NewItemPlaceholder. What I have not found out is how to remove that or even why it is added to the ObservableCollection :o(</p>