protected function validateConvertionRateCurrency()
    {
        $field = 'conversion_rate';
        $value = $this->getSubmitted($field);

        if (!isset($value)) {
            return null;
        }

        $label = $this->translation->text('Conversion rate');

        if (empty($value) || strlen($value) > 10) {
            $this->setErrorLengthRange($field, $label, 1, 10);
            return false;
        }

        if (preg_match('/^[0-9]\d*(\.\d+)?$/', $value) !== 1) {
            $this->setErrorInvalid($field, $label);
            return false;
        }

        return true;
    }