@Override
  public void saveTo(@NotNull DataOutput out,
                     @NotNull DataExternalizer<? super Value> externalizer) throws IOException {
    DataInputOutputUtil.writeINT(out, size());

    for (final InvertedIndexValueIterator<Value> valueIterator = getValueIterator(); valueIterator.hasNext(); ) {
      final Value value = valueIterator.next();
      externalizer.save(out, value);

      final Object fileSetObject = valueIterator.getFileSetObject();
      storeFileSet(out, fileSetObject);
    }
  }
@Override
  public void saveTo(@NotNull DataOutput out,
                     @NotNull DataExternalizer<? super Value> externalizer)