docs: static void rightPadString(StringBuilder builder, char padding, int multipleOf) {
      if (builder == null) {
        throw new IllegalArgumentException("Builder input must not be empty.");
      }
      if (multipleOf < 2) {
        throw new IllegalArgumentException("Multiple must be greater than one.");
      }
      int needed = multipleOf - (builder.length() % multipleOf);
      if (needed < multipleOf) {
        for (int i = needed; i > 0; i--) {
          builder.append(padding);
        }
      }
    }