public final void doesNotContainKey(@Nullable Object key) {
    check("keySet()").that(checkNotNull(actual).keySet()).doesNotContain(key);
  }
@Test
  public void doesNotContainKey() {
    ImmutableMap<String, String> actual = ImmutableMap.of("kurt", "kluever");
    assertThat(actual).doesNotContainKey("greg");
    assertThat(actual).doesNotContainKey(null);
  }