title: Binding ComboBox to Enum throw exception
body: <p>Didn't find out why this is not working :</p>
  
  <p>I have a <code>ComboBox</code> in a <code>UserControl</code> where its <code>ItemSource</code> bind to an <code>Enum</code> using <code>ObjectDataProvider</code> :</p>
  
  <pre><code>xmlns:ViewModels="clr-namespace:CMiX.ViewModels"
  xmlns:System="clr-namespace:System;assembly=mscorlib"
  
  &lt;UserControl.Resources&gt;
      &lt;ResourceDictionary&gt;
          &lt;ObjectDataProvider x:Key="Blend" MethodName="GetValues" ObjectType="{x:Type System:Enum}"&gt;
              &lt;ObjectDataProvider.MethodParameters&gt;
                  &lt;x:Type TypeName="ViewModels:BlendMode"/&gt;
              &lt;/ObjectDataProvider.MethodParameters&gt;
          &lt;/ObjectDataProvider&gt;
      &lt;/ResourceDictionary&gt;
  &lt;/UserControl.Resources&gt;
  
  
  &lt;ComboBox
      SelectedItem="{Binding BlendMode}"
      ItemsSource="{Binding Source={StaticResource Blend}}"&gt;
  &lt;/ComboBox&gt;
  </code></pre>
  
  <p>The Enum is fairly simple :</p>
  
  <pre><code>namespace CMiX.ViewModels
  {
      public enum BlendMode
      {
          Normal,
          Add,
          Subtract
      };
  }
  </code></pre>
  
  <p>Finally the <code>SelectedItem</code> bind to the <code>ViewModel</code> that carry the property <code>BlendMode</code> :</p>
  
  <pre><code>private BlendMode _blendMode;
  public BlendMode BlendMode
  {
      get =&gt; _blendMode;
      set =&gt; SetAndNotify(ref _blendMode, value);
  }
  </code></pre>
  
  <p>Now if I want to run the application I got this :</p>
  
  <pre><code>System.NullReferenceException: 'Object reference not set to an instance of an object.'
  
  Set property 'System.Windows.ResourceDictionary.Source' threw an exception.'
  </code></pre>
  
  <p>Unfortunately I really don't know why.</p>