public function toPrivateArray()
    {
        return array(
            'number' => $this->getNumber(),
            'holder_name' => $this->getHolderName(),
            'expiration_year' => $this->getExpirationYear(),
            'expiration_month' => $this->getExpirationMonth(),
            'security_code' => $this->getSecurityCode(),
        );
    }