assertThrows(
        UnsupportedOperationException.class,
        () -> map.headMap("r", false).tailMap("m", true).keySet().add("a"));
  }

  @GwtIncompatible // NavigableMap
  public void testAsMapNavigableEmpty() {
    NavigableSet<String> strings = ImmutableSortedSet.of();
    NavigableMap<String, Integer> map = Maps.asMap(strings, LENGTH_FUNCTION);
    assertThat(map.entrySet()).isEmpty();
    assertTrue(map.isEmpty());