4,
        "four");
    assertMapEquals(
        ImmutableBiMap.of("one", 1, "two", 2, "three", 3, "four", 4, "five", 5),
        "one",
        1,
        "two",
        2,
        "three",
        3,
        "four",
        4,
        "five",
        5);
    assertMapEquals(
        ImmutableBiMap.of("one", 1, "two", 2, "three", 3, "four", 4, "five", 5).inverse(),
        1,
        "one",

        ImmutableSortedMap.of("one", 1, "two", 2, "three", 3, "four", 4),
        "four",
        4,
        "one",
        1,
        "three",
        3,
        "two",
        2);
    assertMapEquals(
        ImmutableSortedMap.of("one", 1, "two", 2, "three", 3, "four", 4, "five", 5),
        "five",
        5,
        "four",
        4,
        "one",
        1,
        "three",

        4,
        "four");
    assertMapEquals(
        ImmutableBiMap.of("one", 1, "two", 2, "three", 3, "four", 4, "five", 5),
        "one",
        1,
        "two",
        2,
        "three",
        3,
        "four",
        4,
        "five",
        5);
    assertMapEquals(
        ImmutableBiMap.of("one", 1, "two", 2, "three", 3, "four", 4, "five", 5).inverse(),
        1,
        "one",

            .put("three", 3)
            .put("one", 1)
            .put("five", 5)
            .put("four", 3)
            .put("four", 5)
            .put("four", 4) // this should win because it's last
            .put("two", 2);
    assertMapEquals(
        builder.buildKeepingLast(), "one", 1, "two", 2, "three", 3, "four", 4, "five", 5);
    try {
      builder.buildOrThrow();

            .put("three", 3)
            .put("one", 1)
            .put("five", 5)
            .put("four", 3)
            .put("four", 5)
            .put("four", 4) // this should win because it's last
            .put("two", 2);
    assertMapEquals(
        builder.buildKeepingLast(), "one", 1, "two", 2, "three", 3, "four", 4, "five", 5);
    try {
      builder.buildOrThrow();

        ImmutableSortedMap.of("one", 1, "two", 2, "three", 3, "four", 4),
        "four",
        4,
        "one",
        1,
        "three",
        3,
        "two",
        2);
    assertMapEquals(
        ImmutableSortedMap.of("one", 1, "two", 2, "three", 3, "four", 4, "five", 5),
        "five",
        5,
        "four",
        4,
        "one",
        1,
        "three",

          // Three byte characters
          THREE_BYTE_ROUNDTRIPPABLE_CHARACTERS;

  // 1,048,576 [chars 0x10000L to 0x10FFFF]
  private static final long FOUR_BYTE_ROUNDTRIPPABLE_CHARACTERS = 0x10FFFF - 0x10000L + 1;

  // 289,571,839
  private static final long EXPECTED_FOUR_BYTE_ROUNDTRIPPABLE_COUNT =
      // All one byte characters
      (long) Math.pow(EXPECTED_ONE_BYTE_ROUNDTRIPPABLE_COUNT, 4)
          +

          // Three byte characters
          THREE_BYTE_ROUNDTRIPPABLE_CHARACTERS;

  // 1,048,576 [chars 0x10000L to 0x10FFFF]
  private static final long FOUR_BYTE_ROUNDTRIPPABLE_CHARACTERS = 0x10FFFF - 0x10000L + 1;

  // 289,571,839
  private static final long EXPECTED_FOUR_BYTE_ROUNDTRIPPABLE_COUNT =
      // All one byte characters
      (long) Math.pow(EXPECTED_ONE_BYTE_ROUNDTRIPPABLE_COUNT, 4)
          +

        if (!decodeIpv4Suffix(input, groupOffset, limit, address, b - 2)) return null
        b += 2 // We rewound two bytes and then added four.
        break
      } else {
        return null // Wrong delimiter.
      }
    }

    // Read a group, one to four hex digits.
    var value = 0
    groupOffset = i
    while (i < limit) {
      val hexDigit = input[i].parseHexDigit()

  private static final Iterable<@Nullable Integer> ITERABLE_1_NULL_2 = Arrays.asList(1, null, 2);
  private static final Iterable<@Nullable Integer> ITERABLE_FOUR_NULLS =
      Arrays.asList((Integer) null, null, null, null);

  public void testNoSpecialNullBehavior() {
    checkNoOutput(J, ITERABLE_);
    checkResult(J, ITERABLE_1, "1");
    checkResult(J, ITERABLE_12, "1-2");