I am using MongoDB as a database in Spring Boot. But I am getting a problem while adding the data

These are my Entities:-

This is my rider Rider entity

package com.app.enities;

import lombok.*;
import org.springframework.data.annotation.Id;
import org.springframework.data.mongodb.core.mapping.Document;

import java.util.List;

@Document(collection = "Rider")
@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
@ToString(callSuper = true)
public class Rider {
    @Id
    private String id;
    private String firstName;
    private String lastName;
    private String shortCred;
    private Team teamName;
    private List<Sponsor> sponsorList; //Enum
}

This is my team entity where I am adding information about a Team

package com.app.enities;

import lombok.*;
import org.springframework.data.annotation.Id;
import org.springframework.data.mongodb.core.mapping.Document;

@Document
@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
@ToString(callSuper = true)
public class Team {
    @Id
    private String id;
    private String name;
    private Bikes bike; //Enum

}

I am adding data in form of JSON. but as the id will get auto-generated, I am not providing any kind of Id:-

{
    "firstName": "Marc",
    "lastName": "Marquez",
    "shortCred": "MM93",
    "teamName": {
        "name": "Gresini Racing",
        "bike": "DUCATI"
    },
    "sponsorList": [
        "REDBULL",
        "SHOEI",
        "ALPINESTAR",
        "ESTRELLA_GALICIA",
        "SAMSUNG"
    ]
}

But as you can see in the below response (which i have got in return after .save(newRider) method) That Rider id is getting auto generate but team id is not getting auto generate.

{
    "id": "65c731de83a0e43d7526c880",
    "firstName": "Marc",
    "lastName": "Marquez",
    "shortCred": "MM93",
    "teamName": {
        "id": null, <--- null value here
        "name": "Gresini Racing",
        "bike": "DUCATI"
    },
    "sponsorList": [
        "REDBULL",
        "SHOEI",
        "ALPINESTAR",
        "ESTRELLA_GALICIA",
        "SAMSUNG"
    ]
}

This is first time I am using MongoDb with spring so I don’t know how association between tables work or that if it is even a thing to associate to table like we do in sql using @OneToOne or @ManyToOne etc.