code: public void removeAttribute(String name) {
          if (name == null) {
              throw new NullPointerException("don't set a NULL named attribute");
          }
          synchronized (mutex) {
              window.remove(name);
              if (deleteAttributes == null) {
                  deleteAttributes = new HashSet<String>(4);
                  deleteAttributes.add(name);
              }
          }
      }
docs: 实际删除私有属性，如果是窗口共有的portal属性，只是在本窗口中做删除标志，其他窗口还能正常获取
  
  @param name Name of the attribute to remove