spring mongodb - aggregation pipeline into java

I wrote the following aggregation pipeline that returns the most liked items in my users collection

db.users.aggregate([
  {$unwind: "$favoriteItems"},
  {$group: {
    _id: "$favoriteItems" ,
    likes: { $sum: 1 }
  }},
  {$sort: { likes: -1 }}
])

Here is a prototype document from my users collection:

{
  "_id": "5a6df13552f42a34dcca9aa6",
  "username": "user1",
  "favoriteItems": [
    {
      "_id": "5a0c6b2dfd3eb67969316d6d",
      "name": "item1"
    },
    {
      "_id": "5a0c680afd3eb67969316d0b",
      "name": "item2"
    }
  ]
}

This is my attempt at doing the same in java:

public void getMostLikedItems () {
        UnwindOperation unwind = Aggregation.unwind("favoriteItems");
        GroupOperation group = Aggregation.group("favoriteItems").sum("1").as("likes");
        SortOperation sort = Aggregation.sort(Sort.Direction.DESC, "likes");

        Aggregation aggregation = newAggregation(unwind, group, sort);
        AggregationResults<LikedItem > result = mongoTemplate.aggregate(aggregation, "users", LikedItem .class);
        for (LikedItem s: result) {
            System.out.println(s.getId() + ": " + s.getValue());
        }
    }

This is not yielding any output. What am i missing here?

EDIT LikedItem.java

public class LikedItem {

    private Item id;
    private float value;
    // empty and full constructor + getters and setters

}

EDIT 2 Item class

public class Item{
    @Id
    private String id;
    private String name;
    private String city;
    @GeoSpatialIndexed(type= GeoSpatialIndexType.GEO_2DSPHERE)
    private GeoJsonPoint location;

    public Shop() { super(); }
    // full constructor + getters and setters
}