code: public static boolean isValidCardNumber(@Nullable String cardNumber) {
          String normalizedNumber = StripeTextUtils.removeSpacesAndHyphens(cardNumber);
          return isValidLuhnNumber(normalizedNumber) && isValidCardLength(normalizedNumber);
      }
docs: Checks the input string to see whether or not it is a valid card number, possibly
  with groupings separated by spaces or hyphens.
  
  @param cardNumber a String that may or may not represent a valid card number
  @return {@code true} if and only if the input value is a valid card number