import org.hibernate.annotations.GenericGenerator;
 
import javax.persistence.*;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collection;
 
@Entity
@Table(name = "user")
    public class User implements Serializable{
    private Long id;
    private String name;
    private String email;
    private String password;
    @Id
    @GeneratedValue(generator = "increment")
    @GenericGenerator(name= "increment", strategy= "increment")
    public Long getId() {
        return id;
    }
 
    public void setId(Long id) {
        this.id = id;
    }
 
    @Column(name = "name")
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    @Column(name = "email")
    public String getEmail() {
        return email;
    }
 
    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", email='" + email + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
 
    public void setEmail(String email) {
        this.email = email;
    }
 
    @Column(name = "password")
    public String getPassword() {
        return password;
    }
 
    public void setPassword(String password) {
        this.password = password;
    }
 
 
}

@Service
public class UserService {
 
    @Autowired
    private UserDAO userDao;
 
    //добавить User
    public User addUser(User user)
    {
        User savedUser =userDao.saveAndFlush(user);
        return savedUser;
    }
}

@Repository
public interface UserDAO extends JpaRepository<User, Long> {
 
}

public class TestUserService {
    UserService service = new UserService();
 
    @Test
    public void testSaveRecord() throws Exception {
        //создаём юзера для записи в БД
        User user = new User();
        user.setId((long)1);
        user.setName("name");
        user.setEmail("email");
        user.setPassword("password");
        //Записали в БД
        User userSaved = service.addUser(user);
        //Вывели записанную в БД запись
        System.out.println(userSaved);
    }
 
 
}

public class Main {
 
    public static void main(String[] args) {
 
        TestUserService testUserService=new TestUserService();
        try {
            testUserService.testSaveRecord();
        }catch (Exception ex)
        {
           ex.printStackTrace();
        }
 
 
    }
 
}

java.lang.NullPointerException
at com.insart.tasker.services.UserService.addUser(UserService.java:18)
at test.TestUserService.testSaveRecord(TestUserService.java:19)
at Main.main(Main.java:9)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)