[Hibernate] Удалить сущность с null constraint

    @Override
    @Transactional
    public void deleteById(Model model, long playlistId) {
        Playlist playlist = playlistDao.findById(playlistId);
 
        Authentication auth = SecurityContextHolder.getContext().getAuthentication();
        User currentUser = userService.findByUsername(auth.getName());
 
        //Delete all notes which are associated with the videos of the playlist
        List<Video> videosOfThePlaylist = videoService.findAllByPlaylist(playlist);
        for(Video video: videosOfThePlaylist) {
            videoNoteService.removeAllByVideo(video);
        }
 
        videoService.removeAllByPlaylist(playlist);
 
        playlistDao.delete(playlistId);
        currentUser.getPlaylists().remove(playlist);
 
        Set<Playlist> playlistList = playlistDao.findAllByUsers(currentUser);
        model.addAttribute("listOfPlaylists", playlistList);
    }

@Entity
@Table(name = "playlists")
public class Playlist {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;
 
    @Column(name = "name")
    private String name;
 
    @Column(name = "channel")
    private String channel;
 
    @Column(name = "link")
    private String link;
 
    @Column(name = "amount_of_completed_videos")
    private int amountOfCompletedVideos = 0;
 
    @Column(name = "amount_of_videos")
    private int amountOfVideos;
 
    @ManyToMany(mappedBy = "playlists")
    private Set<User> users;
 
    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "playlist")
    private Set<Video> videos = new HashSet<>();
 
    @ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    @JoinColumn(name = "subject_id", nullable = false)
    private Subject subject;
 
    //constructors
    //getters-setters
}

@Entity
@Table(name = "subjects")
public class Subject {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;
 
    @Column(name = "title")
    private String title;
 
    @ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    @JoinColumn(name = "user_id", nullable = false)
    private User user;
 
    @Cascade(org.hibernate.annotations.CascadeType.DELETE)
    @OneToMany(mappedBy = "subject", orphanRemoval = true)
    private Set<Playlist> playlists;
 
    //constructors
    //getters-setters
}

@Entity
@Table(name = "users")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
 
    @Column(name = "username")
    private String username;
 
    @Column(name = "pass")
    private String password;
 
    @Transient
    private String confirmPassword;
 
    @ManyToMany
    @JoinTable(name = "user_roles", joinColumns = @JoinColumn(name = "user_id"),
            inverseJoinColumns = @JoinColumn(name = "role_id"))
    private Set<Role> roles;
 
    @ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinTable(name = "users_playlists", joinColumns = @JoinColumn(name = "user_id"),
            inverseJoinColumns = @JoinColumn(name = "playlist_id"))
    private Set<Playlist> playlists;
 
    @OneToMany(fetch = FetchType.LAZY, mappedBy = "user")
    private Set<Subject> subjects;
 
    //constructors
    //getters-setters
}

    @Override
    @Transactional
    public void deleteById(Model model, long playlistId) {
        Playlist playlist = playlistDao.findById(playlistId);
 
        Authentication auth = SecurityContextHolder.getContext().getAuthentication();
        User currentUser = userService.findByUsername(auth.getName());
 
        //Delete all notes which are associated with the videos of the playlist
        List<Video> videosOfThePlaylist = videoService.findAllByPlaylist(playlist);
        for(Video video: videosOfThePlaylist) {
            videoNoteService.removeAllByVideo(video);
        }
 
        videoService.removeAllByPlaylist(playlist);
 
        currentUser.getPlaylists().remove(playlist);
        playlist.getUsers().remove(currentUser);
        
        playlistDao.delete(playlistId);
 
        Set<Playlist> playlistList = playlistDao.findAllByUsers(currentUser);
        model.addAttribute("listOfPlaylists", playlistList);
    }

@Entity
@Table(name = "videos")
public class Video {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;
 
    @Column(name = "title")
    private String title;
 
    @Column(name = "video_code")
    private String videoCode;
 
    @Column(name = "duration")
    private String duration;
 
    @Column(name = "is_completed")
    private boolean isCompleted;
 
    @Column(name = "level_of_understanding")
    private int levelOfUnderstanding;
 
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "playlist_id", nullable = false)
    private Playlist playlist;
 
    @OneToMany(fetch = FetchType.LAZY, mappedBy = "video")
    private Set<VideoNote> notes = new HashSet<>();
 
    //constructors
    //getters-setters
}

@Entity
@Table(name = "video_notes")
public class VideoNote {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;
 
    @Column(name = "note")
    private String note;
 
    @Column(name = "date")
    private String date;
 
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "video_id", nullable = false)
    private Video video;
 
    //constructors
    //getters-setters
}