Many to One Relationship returns NULL List of Child Object - spring-boot

Question

I have 2 classes. USER class & ORDER class.
Order class has User object with #ManyToOne relationship.
When the RestController retrieves the Order object post insertion of Order object using #PostMapping,it returns null value for nested User object
Rest Controller
#RestController
public class OrderController {
#PersistenceContext
EntityManager entityManager;
#Transactional
#PostMapping(value = "api/v1/create/order")
public Order createOrder(#RequestBody Order order){
entityManager.persist(order);
return order;
}
}
Order class
#Entity
#Table(name = "booking_order")
public class Order {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
Integer orderID;
#Column
String transactionAmount;
#Column
#CreationTimestamp
#Temporal(TemporalType.TIMESTAMP)
Date bookingTimestamp;
#ManyToOne
User user;
public Order(){}
public Integer getOrderID() {
return orderID;
}
public void setOrderID(Integer orderID) {
this.orderID = orderID;
}
public String getTransactionAmount() {
return transactionAmount;
}
public void setTransactionAmount(String transactionAmount) {
this.transactionAmount = transactionAmount;
}
public Date getBookingTimestamp() {
return bookingTimestamp;
}
public void setBookingTimestamp(Date bookingTimestamp) {
this.bookingTimestamp = bookingTimestamp;
}
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
}
User Class
#Entity
#Table(name = "user")
public class User {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
Integer id;
#Column(unique = true)
String username;
#Column
String password;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
}
Input JSON
{
"transactionAmount" : "100.50",
"user":{
"id":1
}
}
Order Response
{
"orderID": 1,
"transactionAmount": "100.50",
"bookingTimestamp": "2019-05-15T20:44:43.234+0000",
"user": {
"id": 1,
"username": null,
"password": null
}
}