Error on saving entity says attribute reference unknown entity - spring-boot

Question

i have created multiple entities having many to one relations when i try to save the user by adding a child book object i am getting an error that the booking's attribute schedule is referencing to an unknown entity. the error is "#OneToOne or #ManyToOne on com.demo.flightmanagement.entity.Booking.schedule references an unknown entity: com.demo.flightmanagement.entity.Schedule"
this is airport entity:
#Entity
public class Airport {
#Id
private int id;
#OneToMany(cascade = CascadeType.ALL,mappedBy = "airport")
private List<Schedule> schedules = new ArrayList<Schedule>();
}
this is schedule entity:
#Entity
public class Schedule {
#Id
private int id;
#OneToMany(mappedBy = "schedule")
private List<Booking> bookings = new ArrayList<Booking>();
#ManyToOne(targetEntity = Airport.class)
#JoinColumn(name="airport_id")
private Airport airport;
}
this is user entity
#Entity
public class User {
#Id
private int id;
private String userName;
private String password;
#OneToMany(cascade = CascadeType.ALL,mappedBy = "user")
private List<Booking> bookings = new ArrayList<Booking>();
}
this is booking entity
#Entity
public class Booking {
#Id
#GeneratedValue
private int id;
#ManyToOne
#JoinColumn(name = "user_id")
private User user;
#ManyToOne
#JoinColumn(name = "schedule_id")
private Schedule schedule;
}
this is main calling class
#SpringBootApplication
public class JwtExamplesApplication {
#Autowired
private UserRepo repo;
#PostConstruct
public void initUsers() {
User u = new User(1, "abc", "def");
Schedule s = new Schedule(22, null);
Booking b = new Booking (u, s);
List<Booking> l = new ArrayList<Booking>();
l.add(b);
u.setBookings(l);
repo.save(u);
}
public static void main(String[] args) {
SpringApplication.run(JwtExamplesApplication.class, args);
}
}
this is user repository for saving
#Repository
public interface UserDao extends JpaRepository<User, BigInteger> {
}