title: How to set first index as blank in combobox
body: <p>I have a combobox that is bound with a datasource. In this combobox I  have to add a blank field at index 0.</p>
  
  <p>I have written following code for getting records.</p>
  
  <pre><code> public List&lt;TBASubType&gt; GetSubType(int typ)
          {
              using (var tr = session.BeginTransaction())
              {
                  try
                  {
                      List&lt;TBASubType&gt; lstSubTypes = (from sbt in session.Query&lt;TBASubType&gt;()
                                                      where sbt.FType == typ
                                                      select sbt).ToList();
  
  
                      tr.Commit();
                      return lstSubTypes;
                  }
                  catch (Exception ex)
                  {
                      CusException cex = new CusException(ex);
                      cex.Write();
                      return null;
                  }
              }
          }
  </code></pre>
  
  <p>After this it bind with combobox with data binding source as below code.</p>
  
  <pre><code>M3.CM.BAL.CM CMobj = new M3.CM.BAL.CM(wSession.CreateSession());
                  lstSubTypes = CMobj.GetSubType(type);
                  this.tBASubTypeBindingSource.DataSource = lstSubTypes;
  </code></pre>