Help needed on Ticket : Get comments

I added below code in getMovie():

List pipeline = new ArrayList<>();
// match stage to find movie
Bson match = Aggregates.match(eq("_id", new ObjectId(movieId)));
pipeline.add(match);
// TODO> Ticket: Get Comments - implement the lookup stage that allows the comments to
// retrieved with Movies.
Bson lookUp = Aggregates.lookup(“comments”,"_id",“movie_id”,“comments”);
pipeline.add(lookUp);
Bson unwind = Aggregates.unwind("$comments");
pipeline.add(unwind);
Bson sort = Aggregates.sort(Sorts.descending(“comments.date”));
pipeline.add(sort);
List movies = new ArrayList();
moviesCollection.aggregate(pipeline).into(movies);

List ‘movies’ in last line has 2 documents sorted on date basis for email id ‘573a1390f29313caabcd418c’. So this seems to be in line what we need.
So I just need to group the documents.

So I add following after sort:

Bson groupCommentsSet = Aggregates.group("$comments.movie_id", Accumulators.addToSet(“comments”, “$comments”));
pipeline.add(groupCommentsSet);

But this doesn’t work. Comments are in ascending order of dates. Moreover, other fields are also lost.

Anyone, faced this issue?

Hi!
Do not use unwind and sort stage in this tiket