protected function validateStoreTimezoneInstall()
    {
        $field = 'store.timezone';

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

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

        if (empty($value)) {
            $this->setSubmitted($field, date_default_timezone_get());
            return true;
        }

        $timezones = gplcart_timezones();

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

        return true;
    }