title: Deselect combobox item
body: <p>I have a databound combobox:</p>
  
  <pre><code>using(DataContext db = new DataContext())
  {
      var ds = db.Managers.Select(q=&gt; new { q.ManagerName, q.ManagerID});
  
      cmbbx_Managers.BindingContext = new BindingContext();
      cmbbx_Managers.DataSource = ds;
      cmbbx_Managers.DisplayMember = "ManagerName";
      cmbbx_Managers.ValueMember = "ManagerID";
  }
  </code></pre>
  
  <p>When the form loads neither item is selected, but when the user chooses an item it cannot be deselected. I tried to add <code>cmbbx_Managers.items.Insert(0, "none")</code>, but it does not solve the problem, because it is impossible to add a new item to the databound combobox.</p>
  
  <p>How do I allow a user to deselect a <code>combobox</code> item?</p>