assertTrue("containsKey(null) should return true", getMap().containsKey(null));
  }

  @MapFeature.Require(ALLOWS_NULL_VALUES)
  @CollectionSize.Require(absent = ZERO)
  public void testContains_keyWithNullValueContained() {
    initMapWithNullValue();
    assertTrue(
        "containsKey(keyForNullValue) should return true",
        getMap().containsKey(getKeyForNullValue()));
  }