Projection on the _id field returns wrong result when using @MongoId (MongoDB 4.4)

[steschae]

Describe the bug
Executing a MongoDB query against MongoDB 4.4 which contains a projection on the _id field with an entity class using the @MongoId annotation on a string-id field results in returned objects which have incorrect id values. In fact, the id values of all returned objects all have the same value "1".
However, when using the @Id instead of the @MongoId annotation, the same query returns the expected results containing the correct id values.

Expected behavior
The returned objects each have their correct id value.

Actual behavior
When using MongoDB 4.4: The returned objects each have the id value "1"
When using MongoDB 4.2: The returned objects each have their correct id value.

To Reproduce
I have set up an example project with test cases (https://github.com/steschae/spring-data-mongodb-id-projection-bug). The test "MongoDbVersion4_4_Test > should_find_all_person_ids_when_using_mongo_id_annotation" is the one which is failing because of this bug (https://github.com/steschae/spring-data-mongodb-id-projection-bug/runs/2818935410#step:4:33).

To reproduce, 1. create an entity class using the @MongoId annotation

@Data
public class Person {
    @MongoId
    private String id;
}

2. Create a query with a projection on the _id field:

public interface PersonRepository extends CrudRepository<PersonWithMongoId, String> {
    @Query(value="{}", fields = "{ _id : 1 }")
    List<Person> findAllIds();
}

or

final var query = new Query();
query.fields().include(ID);
mongoTemplate.find(query, Person.class);

3. When executing the query, all returned objects have the value "1" in the id field.

Configuration/Environment/Context
MongoDB 4.4
org.springframework.data:spring-data-mongodb:3.2.1
org.mongodb:mongodb-driver-sync:4.2.3

Additional information
With MongoDB 4.4 the behaviour of projection documents in MongoDB queries has changed:
(https://docs.mongodb.com/manual/release-notes/4.4-compatibility/#projection-compatibility-changes)

The query is translated to db.getCollection("persons").find({}, {"_id": "1"}) (the value of the _id projection is a string). This worked with MongoDB 4.2, but with MongoDB 4.4 the string value "1" in the projection causes the id value of the returned documents to be overidden with this value "1".
This happens somewhere in org.springframework.data.mongodb.core.convert.QueryMapper#getMappedValue, org.springframework.data.mongodb.core.convert.QueryMapper#convertId.

[christophstrobl]

thanks for reporting - we'll look into this.