Custom user is null when i is defined in another tabel with springboot

  public Order placeOrder(OrderDTO orderDTO, CustomUser customUser) {

        final Order order = new Order();
        order.setCustomUser(customUser);
        order.setStatus("placed");
        order.setOrderDate(LocalDate.now());
        order.setOrderProducts(new HashSet<>());
        orderRepository.save(order);

  public Order placeOrder(OrderDTO orderDTO, CustomUser customUser) {

        final Order order = new Order();
        order.setCustomUser(customUser);
        order.setStatus("placed");
        order.setOrderDate(LocalDate.now());
        order.setOrderProducts(new HashSet<>());
        orderRepository.save(order);

public class CustomUser {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String firstname;

    private String lastname;

    private String email;
    @Column(name ="password", nullable = false )

    private String password;

    private UserRole userRole;

public class CustomUser {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String firstname;

    private String lastname;

    private String email;
    @Column(name ="password", nullable = false )

    private String password;

    private UserRole userRole;