code: function(cls) {
          var me = this,
              isEmpty = !cls || !cls.length,
              iconCmp = me.iconCmp;
  
          me.iconCls = cls;
          if (!me.iconCmp && !isEmpty) {
              me.initIconCmp();
              me.insert(0, me.iconCmp);
          } else if (iconCmp) {
              if (isEmpty) {
                  me.iconCmp.destroy();
                  delete me.iconCmp;
              } else {
                  iconCmp.removeCls(iconCmp.iconCls);
                  iconCmp.addCls(cls);
                  iconCmp.iconCls = cls;
              }
          }
      }
docs: Sets the CSS class that provides the icon image for this header.  This method will replace any existing
  icon class if one has already been set.
  @param {String} cls The new CSS class name