title: Combobox <Extjs4 - Empty line
body: <p>Before starting I am sorry with my english.. I don't speak it well .. 
  So I have a problem with the Combobox in ExtJS4 .. I tried to add a empty line in my combobox list but It's not ok .. i have the list with a empty line but when I trie to select it I can't.. so if someone can help me or have an example please</p>
  
  <pre><code>Ext.require([
      'Ext.form.*',
      'Ext.data.*',
      'Ext.tip.QuickTipManager'
  ]);
  
  Ext.onReady(function () {
      Ext.QuickTips.init();
  
  
      var form = Ext.create('Ext.form.Panel', {
          renderTo: 'docbody',
          title: ' ',
          autoHeight: true,
          width: 600,
          bodyPadding: 10,
          defaults: {
              anchor: '100%',
              labelWidth: 100
          },
          items: [{
              xtype: 'fieldcontainer',
              combineErrors: true,
              msgTarget: 'side',
              fieldLabel: ' Name',
              items: [{
                  width: 50,
                  xtype: 'combo',
                  mode: 'local',
                  triggerAction: 'all',
                  forceSelection: true,
                  editable: false,
                  selectOnFocus: true,
                  name: 'title',
                  displayField: 'name',
                  valueField: 'value',
                  tpl: '&lt;tpl for="."&gt;&lt;div class="x-combo-list-item"&gt;{name:defaultValue("--")}&lt;/div&gt;&lt;/tpl&gt;',
                  queryMode: 'local',
                  store: Ext.create('Ext.data.Store', {
                      fields: ['name', 'value'],
                      data: [{
                          name: 'Mvr',
                          value: 'mr'
                      }, {
                          name: 'Mrs',
                          value: 'mrs'
                      }, {
                          name: 'Miss',
                          value: 'miss'
                      }],
                      listeners: {
                          'load': function (store, records, options) {
                              this.insert(0, '--');
                          }
                      }
                  })
              }]
          }]
  
      });
  });
  </code></pre>