@MapFeature.Require(ALLOWS_NULL_KEY_QUERIES)
  public void testKeySetContainsNullKeyAbsent() {
    assertFalse(multimap().keySet().contains(null));
  }

  @MapFeature.Require(SUPPORTS_REMOVE)
  public void testKeySetRemovePropagatesToMultimap() {
    int key0Count = multimap().get(k0()).size();
    assertEquals(key0Count > 0, multimap().keySet().remove(k0()));
    assertEquals(getNumElements() - key0Count, multimap().size());
    assertGet(k0());