private function convertNumber($sign, $integer, $fractions)
    {
        try {
            $result = implode('', $this->convertInteger($this->source->splitString($integer)));

            if ($fractions !== null) {
                $result .= '.' . implode('', $this->convertFractions($this->source->splitString($fractions)));
            }
        } catch (DigitList\InvalidDigitException $ex) {
            return false;
        }

        return $sign . $result;
    }