docs: @Override
      public void removeNotificationHandler(String serviceName, NotificationHandler handler) throws ServiceException {
  
          ServiceInstanceUtils.validateManagerIsStarted(isStarted.get());
          ServiceInstanceUtils.validateServiceName(serviceName);
          if (handler == null) {
              throw new ServiceException(ErrorCode.SERVICE_DIRECTORY_NULL_ARGUMENT_ERROR,
                      ErrorCode.SERVICE_DIRECTORY_NULL_ARGUMENT_ERROR.getMessageTemplate(),
                      "NotificationHandler");
          }
          
          getLookupService().removeNotificationHandler(serviceName, handler);
      }