/**
  * Returns whether the current page is valid.
  *
  * @return <code>false</code> if the current page is not valid, or or <code>true</code> if the
  *     current page is valid or there is no current page
  */
 protected boolean isCurrentPageValid() {
   if (currentPage == null) {
     return true;
   }
   return currentPage.isValid();
 }