Flex中如何去掉Tree控件默认文件夹图标、叶子节点图标

  .treeStyte{
    selectionColor: #417597;
    /* 去掉默认图标 */
    folderClosedIcon: ClassReference(null);
            folderOpenIcon: ClassReference(null);
            defaultLeafIcon: ClassReference(null);  
            disclosureOpenIcon:ClassReference(null);
           
            /*为默认、打开、关闭、有子项等几个状态添加不同的ico*/
   defaultLeafIcon: Embed(source="img/tree/user_man.png");
  /* folderOpenIcon: Embed(source="img/tree/usergroup.png"); */
   folderClosedIcon: Embed(source="img/tree/usergroup.png");
   disclosureOpenIcon: Embed(source="img/tree/user_men.png");
   }