code: @VisibleForTesting
      String stripSeparators(final String cardNumber) {
          final int length = cardNumber.length();
          final char[] result = new char[length];
          int count = 0;
          char cur;
          for (int i = 0; i < length; i++) {
              cur = cardNumber.charAt(i);
              if (!(cur == ' ' || cur == '-')) {
                  result[count++] = cur;
              }
          }
          if (count == length) {
              return cardNumber;
          }
          return new String(result, 0, count);
      }
docs: Remove any ` ` and `-` characters from the given string.
  
  @param cardNumber the number to clean up
  @return if the given string contains no ` ` or `-` characters, the string
  itself is returned, otherwise a new string containing no ` ` or `-`
  characters is returned