src/Common/CreditCard.php
public function getBirthday($format = 'Y-m-d')
    {
        $value = $this->getParameter('birthday');

        return $value ? $value->format($format) : null;
    }
public function getBirthday($format = 'Y-m-d')
    {
        $value = $this->getParameter('birthday');

        return $value ? $value->format($format) : null;
    }
Get the cardholder's birthday.

@return string