} else {
      assertThrows(
          UnsupportedOperationException.class, () -> valueCollection.retainAll(valuesToRetain));
    }
    assertInvariants(map);
  }

  public void testValuesRetainAllNullFromEmpty() {
    Map<K, V> map;
    try {
      map = makeEmptyMap();
    } catch (UnsupportedOperationException e) {
      return;
    }

    Collection<V> values = map.values();