code: protected void validateRequired(String field, String errorKey, String errorMessage) {
  		String value = controller.getPara(field);
  		if (value == null || "".equals(value)) {	// 经测试,form表单域无输入时值为"",跳格键值为"\t",输入空格则为空格" "
  			addError(errorKey, errorMessage);
  		}
  	}
docs: Validate Required. Allow space characters.