code: 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);
        }
      }
    }
docs: Pad a {@link StringBuilder} to a desired multiple on the right using a specified character.
  
  @param builder Builder to pad.
  @param padding Padding character.
  @param multipleOf Number which the length must be a multiple of.
  @throws IllegalArgumentException if {@code builder} is null or {@code multipleOf} is less than
  2.