Столбец "столбец" не может быть нулевым

Я делаю небольшое веб-приложение. В этом приложении я могу регистрировать новых пользователей. У пользователя есть один ролик, а у ролика может быть много пользователей.

Таблица пользователей

Таблица ролей

Если я сделаю INSERT, я хочу, чтобы столбец rol_id был равен «1» (rol: users). Все работает хорошо, когда я работаю с СУБД, но это не так, когда я работаю со Spring, потому что я получаю следующую ошибку

2018-05-01 11:00:43.432 ERROR 9448 --- [nio-8080-exec-7] o.h.engine.jdbc.spi.SqlExceptionHelper   : Column 'rol_id' cannot be null

Мой код такой:

Роликовый стол

@Entity
@Table(name = "roles")
public class Rol implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy= GenerationType.IDENTITY)
    @Column(name = "id_rol", updatable = false, nullable = false)
    private Long id;

    @Column(name = "rol")
    @NotEmpty
    private String rolType;

    @OneToMany(mappedBy= "rol")
    private List<User> users = new ArrayList<>();

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getRol() {
        return rolType;
    }

    public void setRol(String rol) {
        this.rolType = rol;
    }

    public List<User> getUsers() {
        return users;
    }

    public void setUsers(List<User> users) {
        this.users = users;
    }

}

Таблица пользователей

@Entity
@Table(name = "users")
public class User implements Serializable{

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy= GenerationType.IDENTITY)
    @Column(name = "id_user", updatable = false, nullable = false)
    private Long id;

    @Column(name = "name")
    @NotEmpty
    @Length(min= 3, max= 25)
    private String name;

    @Column(name = "surname")
    @NotEmpty
    @Length(min= 2, max=30)
    private String surname;

    @Column(name = "email")
    @NotEmpty
    @Email
    @Length(min=5, max=30)
    private String email;

    @Column(name = "birthdate", nullable = true)
    private String birthdate;

    @Column(name = "created_at")
    @Temporal(TemporalType.DATE)
    @DateTimeFormat(pattern = "yyyy-MM-dd")
    private Date createdAt = new Date();

    @Column(name = "gender")
    @NotEmpty
    @Length(min=4, max=6)
    private String gender;

    @Column(name = "username")
    @NotEmpty
    @Length(min=3, max=20)
    private String username;

    @Column(name = "pass")
    @NotEmpty
    @Length(min=8, max=30)
    private String password;

    @ManyToOne
    @JoinColumn(name = "rol_id")
    private Rol rol;


    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSurname() {
        return surname;
    }

    public void setSurname(String surname) {
        this.surname = surname;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getBirthdate() {
        return birthdate;
    }

    public void setBirthdate(String birthdate) {
        this.birthdate = birthdate;
    }

    public Date getCreatedAt() {
        return createdAt;
    }

    public void setCreatedAt(Date createdAt) {
        this.createdAt = createdAt;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    /* MODOFIQUE ESTO ACA, NO SE SI ESTA BIEN */
    public String getRol() {
        return rol.getRol();
    }

    public void setRol(Rol rol) {
        this.rol = rol;
    }

}

Класс DAO

public interface IUserDAO extends CrudRepository<User, Long>{
}

Интерфейс UserService

public interface IUserService {

    public List<User> findAll();
    public void save(User user);
    public User findOne(Long id);

}

Класс, реализующий UserService

@Service
public class UserServiceImpl implements IUserService{

    @Autowired
    IUserDAO userDAO;

    @Override
    @Transactional(readOnly = true)
    public List<User> findAll() {
        return userDAO.findAll();
    }

    @Override
    @Transactional
    public void save(User user) {
        userDAO.save(user);

    }

    @Override
    @Transactional(readOnly = true)
    public User findOne(Long id) {
        return userDAO.findOne(id);
    }

}

Это мой контроллер

@Controller
@SessionAttributes("user")
public class UserController {

    Constants c = new Constants();

    @Autowired
    IUserService userService;

    @RequestMapping(value= "user/add", method = RequestMethod.GET)
    public String addUser(Model model) {
        User user = new User();
        model.addAttribute("user", user);
        model.addAttribute(c.TITLE, "Add User");
        model.addAttribute(c.ADD_USER);
        return "user-add";
    }

    @RequestMapping(value= "user/add", method = RequestMethod.POST)
    public String addUser(@Valid User user, BindingResult result, Model model, RedirectAttributes ra, SessionStatus status) {
        if (result.hasErrors()) {
            return "redirect:/user/add";
        }

        try {
            userService.save(user);
            status.setComplete();
        } catch(Exception e) {
            return "redirect:/user/list";
        }
        return "user-add";
    }

    @RequestMapping(value= "user/list", method = RequestMethod.GET)
    public String listUsers(Model model) {
        model.addAttribute("users", userService.findAll());
        model.addAttribute(c.TITLE, "Users List");
        model.addAttribute(c.LIST_USER);
        return "user-list";
    }

}

И мой взгляд с тимелистом

<form th:action = "@{/user/add}" method = "POST" th:object = "${user}" style = "width: 70%;">

    <div class = "form-group">
        <label for = "inputName" class = "text-uppercase font-weight-bold">Name</label>
        <input type = "text" class = "form-control" id = "inputName" th:field = "*{name}" autocomplete = "off">
    </div>

    <div class = "form-group">
        <label for = "inputSurname" class = "text-uppercase font-weight-bold">Surname</label>
        <input type = "text" class = "form-control" id = "inputSurname" th:field = "*{surname}" autocomplete = "off">
    </div>

    <div class = "form-group">
        <label for = "inputEmail" class = "text-uppercase font-weight-bold">Email</label>
        <input type = "email" class = "form-control" id = "inputEmail" th:field = "*{email}" autocomplete = "off">
    </div>

    <div class = "form-group">
        <label for = "inputBirthdate" class = "text-uppercase font-weight-bold">Birthdate</label>
        <input type = "date" class = "form-control" id = "inputBirthdate" th:field = "*{birthdate}" autocomplete = "off">
    </div>

    <div class = "form-group mb-5">
        <label for = "inputGender" class = "text-uppercase font-weight-bold">Gender</label>
        <select type = "date" class = "form-control" id = "inputGender" th:field = "*{gender}">
            <option th:value = "other">Other</option>
            <option th:value = "male">Male</option>
            <option th:value = "female">Female</option>
        </select>
    </div>

    <div class = "form-group">
        <label for = "inputUsername" class = "text-uppercase font-weight-bold">Username</label>
        <input type = "text" class = "form-control" id = "inputUsername" th:field = "*{username}" autocomplete = "off">
    </div>

    <div class = "form-group">
        <label for = "inputPassword" class = "text-uppercase font-weight-bold">Password</label>
        <input type = "password" class = "form-control" id = "inputPassword" th:field = "*{password}" autocomplete = "off">
    </div>

    <button type = "submit" class = "btn btn-primary w-100">
        Add User
    </button>
</form>

Все, что я хочу, я устанавливаю равным 1 rol_id, когда делаю вставку. Почему-то работает только в СУБД, а в Spring - нет.

Заранее спасибо.