title: How to make WPF ComboBox default selection to blank
body: <p>I have an <code>enum</code> like:</p>
  
  <pre><code>enum Gender
  {
     Male = 1,
     Female = 2
  }
  </code></pre>
  
  <p>Then I have a <code>Combobox</code> binding to a list of <code>Gender</code>.</p>
  
  <pre><code>&lt;ComboBox ItemSource = 'Binding GenderList, Mode=TwoWay,
                          UpdateSourceTrigger=PropertyChanged'
            SelectItem = 'Binding SelectedGender' /&gt;
  </code></pre>
  
  <p>When user opens the view, how can I make <code>ComboBox</code> selection default to blank? Then after user made a selection, the blank selection is removed from the <code>ComboBox</code> source.</p>
  
  <p>Thanks</p>
  
  <hr>
  
  <p>Thanks all the replies. I fixed my problem by manully assigning the selected item to null.</p>