}
  }

  @Override
  public void testValuesRemoveAllNullFromEmpty() {
    try {
      super.testValuesRemoveAllNullFromEmpty();
    } catch (RuntimeException tolerated) {
      // GWT's HashMap.values().removeAll(null) doesn't throws NPE.
    }
  }

  @Override
  public void testValuesRetainAllNullFromEmpty() {
    try {
      super.testValuesRemoveAllNullFromEmpty();
    } catch (RuntimeException tolerated) {

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

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

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