docs: protected boolean hasFieldError(String fieldname) {
  		if ( StringUtils.isEmpty(fieldname)) {
  			return false;
  		}
  
  		Object action = ActionContext.getContext().getActionInvocation().getAction();
  		// check action instance 'ActionSupport'.
  		if (!(action instanceof ActionSupport)) {
  			return false;
  		}
  
  		ActionSupport asupport = (ActionSupport) action;
  		Map<String, List<String>> fieldErrors = asupport.getFieldErrors();
  		if (CollectionUtils.isEmpty(fieldErrors)) {
  			return false;
  		}
  		List<String> targetFieldErrors = fieldErrors.get(fieldname);
  		if (CollectionUtils.isEmpty(targetFieldErrors)) {
  			return false;
  		}
  
  		return true;
  	}