assertThrows(NullPointerException.class, () -> ImmutableBiMap.of("one", 1, "two", null));
  }

  @SuppressWarnings({"AlwaysThrows", "DistinctVarargsChecker"})
  public void testOfWithDuplicateKey() {
    IllegalArgumentException expected =
        assertThrows(IllegalArgumentException.class, () -> ImmutableBiMap.of("one", 1, "one", 1));
    assertThat(expected).hasMessageThat().contains("one");
  }

    assertThrows(NullPointerException.class, () -> ImmutableSortedMap.of("one", 1, "two", null));
  }

  @SuppressWarnings("DistinctVarargsChecker")
  public void testOfWithDuplicateKey() {
    assertThrows(IllegalArgumentException.class, () -> ImmutableSortedMap.of("one", 1, "one", 1));
  }

  public void testCopyOfEmptyMap() {
    ImmutableSortedMap<String, Integer> copy =