protected function getAccountDigits()
    {
        if (!$this->getWithAccountNumber()) {
            throw new DisabledDataException('account number');
        }
        if ($this->getNotForPayment()) {
            return 'XXXXXXXXX';
        }
        $accountNumber = $this->getAccountNumber();
        if ($accountNumber === '') {
            return $accountNumber;
        }
        $accountDigits = str_replace('-', '', $accountNumber, $replacedHyphens);
        if ($replacedHyphens != 2) {
            throw new PaymentSlipException('Invalid Account number. Does not contain two hyphens.');
        }
        return $accountDigits;
    }