public Map getRootData() {
		for (Scope cur=this; true; cur=cur.parent) {
			if (cur.parent == null) {
				return cur.data;
			}
		}
	}
public Map getRootData ( ) { for ( Scope cur = this ; true ; cur = cur . parent ) { if ( cur . parent == null ) { return cur . data ; } } }
获取顶层作用域 data，可能为 null 值