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");
}