NullPointerException when adding to a List even if the List is instantiated

Question

I am currently trying to add some Roles to my User, however I always get a NullPointerException when I try to do so.

This is my AppUser with the addRole method where the exception happens

@Builder
@AllArgsConstructor
@NoArgsConstructor
@Getter
@Setter
@Entity
public class AppUser {
    @Id
    @SequenceGenerator(
            name = "app_user_id_sequence",
            sequenceName = "app_user_id_sequence"
    )
    @GeneratedValue(
            strategy = GenerationType.SEQUENCE,
            generator = "app_user_id_sequence"
    )
    private Long id;
    @NotBlank
    @Column(nullable = false)
    private String firstName;

    @NotBlank
    @Column(nullable = false)
    private String lastName;

    @Email
    @Column(nullable = false, unique = true)
    private String email;

    @NotBlank
    @Column(nullable = false)
    private String password;

    @ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
    @JoinTable(name = "app_user_roles",
            joinColumns = @JoinColumn(name = "app_user_id"),
            inverseJoinColumns = @JoinColumn(name = "roles_id"))
    private Collection<Role> roles = new ArrayList<>();

    public void addRole (Role role) {
            roles.add(role);
    }
}

And this is the place where I am adding a role to my user

@Component
public class UserSeeder implements CommandLineRunner {
    @Autowired
    private AppUserRepository appUserRepository;
    @Autowired
    private RoleRepository roleRepository;
    private Faker faker = new Faker();

    @Override
    public void run(String... args) throws Exception {
        loadUserData();
    }

    private void loadUserData() {
        if (appUserRepository.count() == 0) {

            roleRepository.findAll().stream().forEach(role -> {
                AppUser appUser = AppUser.builder()
                        .firstName(faker.name().firstName())
                        .lastName(faker.name().lastName())
                        .email(faker.internet().emailAddress())
                        .password("password")
                        .build();
                
                appUser.addRole(role); //Adding the role here
                
                appUserRepository.save(appUser);
            });
        }
    }
}

The error I am getting

java.lang.IllegalStateException: Failed to execute CommandLineRunner
    at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:774) ~[spring-boot-2.7.1.jar:2.7.1]
    at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:755) ~[spring-boot-2.7.1.jar:2.7.1]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) ~[spring-boot-2.7.1.jar:2.7.1]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1306) ~[spring-boot-2.7.1.jar:2.7.1]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1295) ~[spring-boot-2.7.1.jar:2.7.1]
    at com.alex.user.UserApplication.main(UserApplication.java:11) ~[classes/:na]
Caused by: java.lang.NullPointerException: Cannot invoke "java.util.Collection.add(Object)" because "this.roles" is null
    at com.alex.user.AppUser.addRole(AppUser.java:51) ~[classes/:na]
    at com.alex.user.seeders.UserSeeder.lambda$loadUserData$0(UserSeeder.java:43) ~[classes/:na]
    at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1625) ~[na:na]
    at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:762) ~[na:na]
    at com.alex.user.seeders.UserSeeder.loadUserData(UserSeeder.java:35) ~[classes/:na]
    at com.alex.user.seeders.UserSeeder.run(UserSeeder.java:29) ~[classes/:na]
    at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:771) ~[spring-boot-2.7.1.jar:2.7.1]