} else {
      return new MapKeySetGenerator<>(mapGenerator);
    }
  }

  public static class MapKeySetGenerator<K extends @Nullable Object, V extends @Nullable Object>
      implements TestSetGenerator<K>, DerivedGenerator {
    private final OneSizeTestContainerGenerator<Map<K, V>, Entry<K, V>> mapGenerator;
    private final SampleElements<K> samples;