public void testContainsKeyNullAbsent() {
    assertFalse(multimap().containsKey(null));
  }

  @MapFeature.Require(absent = ALLOWS_NULL_KEY_QUERIES)
  public void testContainsKeyNullDisallowed() {
    assertThrows(NullPointerException.class, () -> multimap().containsKey(null));
  }