public function validateSubmitValue($values) {
        foreach ($this->_elements as $element) {
            if (method_exists($element, 'validateSubmitValue')) {
                $value = $values[$element->getName()] ?? null;
                $result = $element->validateSubmitValue($value);
                if (!empty($result) && is_string($result)) {
                    return $result;
                }
            }
        }
    }