@Override
    public <K, V> MultiMaplet<K, V> createSetMultiMaplet(String storageName, Externalizer<K> keyExternalizer, Externalizer<V> valueExternalizer) {
      return new MemoryMultiMaplet<>(() -> (Set<V>)new HashSet<V>());
    }
@Override
    public <K, V> MultiMaplet<K, V> createSetMultiMaplet(String storageName, Externalizer<K> keyExternalizer, Externalizer<V> valueExternalizer)