@Override
    public SampleElements<String> sampleValues() {
      return new SampleElements<>("january", "february", "march", "april", "may");
    }

    @Override
    public Collection<String> createCollection(Iterable<? extends String> values) {
      return Lists.newArrayList(values);
    }

    @Override
    public SampleElements<Entry<String, String>> samples() {
      return new SampleElements<>(

      return createMaybeNavigableKeySet();
    }

    @Override
    Map<K, Collection<V>> createAsMap() {
      return createMaybeNavigableAsMap();
    }

    @Override
    protected Collection<V> createCollection() {
      return factory.get();
    }

    @Override
    <E extends @Nullable Object> Collection<E> unmodifiableCollectionSubclass(
        Collection<E> collection) {