Major Description
(1) The onValidate() method of the CreditCardValidator class returns true for invalid inputs with null or unicode character such as 4\0\0\0\0\0\0\0\0\0\0\0\0\0\0.
(2) Also there is no length check on the input, therefore even invalid length inputs such as 9845 are accepted.
(3) There is no check for invalid issuer identifier, i.e., 840898920205250 is accepted, where 84XXXX is not a valid issuer identifier