Spring Boot MongoDB Lookup not working with ObjectId - mongodb

Question

I've user collection which has role object which has roleId. I also have roles collection which has id.
Now,for each role, I'd like to get the list of users.
Ex:
[
{
"name": "Scott",
"role": {
"roleId": "123432"
}
},
{
"name": "John",
"role": {
"roleId": "123432"
}
},
{
"name": "Scott",
"role": {
"roleId": "556432"
}
}
]
Roles Data:
[
{
"id": "123432"
"name": "admin",
"type": "internal"
},
{
"id": "556432"
"name": "owner",
"type": "external"
},
{
"id": "556432"
"name": "owner",
"type": "internal"
}
]
Now I want to get all the roles of type internal and their related users:
So, the output should be,
[
{
"role": "123432",
"users": [
{
"name": "Scott",
"role": {
"roleId": "123432"
}
},
{
"name": "John",
"role": {
"roleId": "123432"
}
}
],
{
"role": "556432",
"users": []
}
}
]
This is my aggregation in SpringBoort:
LookupOperation lookupOperation = LookupOperation.newLookup().from("roles").localField("roleId")
.foreignField("_id").as("roles");
AggregationOperation match = Aggregation.match(Criteria.where("type").is("internal"));
Aggregation aggregation = Aggregation.newAggregation(lookupOperation, match);
List<UserDTO> results = mongoTemplate.aggregate(aggregation, "users", UserDTO.class).getMappedResults();
This is working great when roleId is in the form of ObjectId(Ex: ObjectId("556432")). But it's not working if it's in String(Ex: "556432").
Can someone help me on this please?