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A beginner Java programmer created an immutable object, but it is not functioning correctly. What is wrong with their code? (Choose from options below)

1public class Car {
2private final String model;
3private String registrationNum;
4
5Car (final String model) {
6    this.model = model;
7}
8
9public final String printModel() {
10    System.out.println(this.model);
11}