code: public static ValueAdaptor register(String className, ValueAdaptor adaptor) {
          if (adaptor == null)
              return customValueAdaptorMap.remove(className);
          return customValueAdaptorMap.put(className, adaptor);
      }
docs: 注册一个自定义ValueAdaptor,若adaptor为null,则取消注册
  @param className 类名
  @param adaptor 值适配器实例,若为null,则取消注册
  @return 原有的值适配器