}

  /**
   * Returns a string representation of the {@code UnsignedLong} value, in base {@code radix}. If
   * {@code radix < Character.MIN_RADIX} or {@code radix > Character.MAX_RADIX}, the radix {@code
   * 10} is used.
   */
  public String toString(int radix) {
    return UnsignedLongs.toString(value, radix);
  }

   * @param radix the radix to use when parsing
   * @return the integer value represented by {@code string} using {@code radix}, or {@code null} if
   *     {@code string} has a length of zero or cannot be parsed as an integer value
   * @throws IllegalArgumentException if {@code radix < Character.MIN_RADIX} or {@code radix >
   *     Character.MAX_RADIX}