Spring Data MongoDB Aggregation.lookup Results Do Not Include Referenced Collection Data

I am using Aggregation.lookup from Spring Data MongoDB to query data from 2 collections, and they are One-To-Many. Data structure and Java code are as followings:

Collection persons:

{ "name": "dave", "pets": [ 111, 112, 113] },
{ "name": "smith", "pets": [ 111, 112 ] },
{ "name": "ahn", "pets": [ 111, 112, 113 ] }

Collection pets

{"petId": 111, "petName": "dog",    "petFood": "Meat"},
{"petId": 112, "petName": "rabbit", "petFood": "carrot"},
{"petId": 114, "petName": "cat",    "petFood": "Fish"},
{"petId": 115, "petName": "fish",   "petFood": "worm"}

Java Models:

@Document("persons")
public class Person {
    @Id
    String id;
    String name;
    @DocumentReference(lazy = false)
    List<Pet> pets;
}

@Document("pets")
public class Pet {
    @Id
    String id;
    String name;
    @DocumentReference(lookup = "{ 'petId' : ?#{#target} }")
    Person person;
}

AggregationOperation match = Aggregation.match(Criteria.where("name").is("smith"));
AggregationOperation query = Aggregation.lookup("pets", "pets", "petId", "pets");
Aggregation aggregation = Aggregation.newAggregation(query, match);

AggregationResults<Person> results = mongoTemplate.aggregate(aggregation,
        mongoTemplate.getCollectionName(Person.class), Person.class);

return results.getMappedResults();

I printed out the executed MongoDB query in the console:

db.persons.aggregate([
  {
    "$lookup": {
      "from": "pets",
      "localField": "pets",
      "foreignField": "petId",
      "as": "pets"
    }
  },
  { "$match": { "name": "smith" } }
])

I run the query in mongo command line, and the result looks good that it includes pets details list:

[
  {
    _id: ObjectId("61f304711b35ae9b874cf800"),
    name: 'smith',
    pets: [
      {
        _id: ObjectId("61f2fe371b35ae9b874cf7f4"),
        petId: 111,
        petName: 'dog',
        petFood: 'Meat'
      },
      {
        _id: ObjectId("61f2fe371b35ae9b874cf7f5"),
        petId: 112,
        petName: 'rabbit',
        petFood: 'carrot'
      }
    ]
  }
]

The problem is, the results from Java code only contains Person data, and the list of pets is empty. Did I miss something in the Java code?

It would be appreciated if someone could help me with this.