protected function validateValueTypePriceRule()
    {
        $field = 'value_type';

        if ($this->isExcluded($field)) {
            return null;
        }

        $value = $this->getSubmitted($field);

        if ($this->isUpdating() && !isset($value)) {
            $this->unsetSubmitted($field);
            return null;
        }

        $types = $this->price_rule->getTypes();

        if (empty($types[$value])) {
            $this->setErrorInvalid($field, $this->translation->text('Value type'));
            return false;
        }

        return true;
    }