code: @NonNull
      @Card.CardBrand
      public static String getPossibleCardType(@Nullable String cardNumber) {
          return getPossibleCardType(cardNumber, true);
      }
docs: Returns a {@link Card.CardBrand} corresponding to a partial card number,
  or {@link Card#UNKNOWN} if the card brand can't be determined from the input value.
  
  @param cardNumber a credit card number or partial card number
  @return the {@link Card.CardBrand} corresponding to that number,
  or {@link Card#UNKNOWN} if it can't be determined