Spring Boot为什么会返回一些值为null的json？

我正在做一个练习游戏。

我有一个连接到MySQL数据库的spring boot / Maven项目。我能够设置一个仅从我的“ allriddles”表中检索所有内容的api。它曾经工作过，但现在api返回一个json，其中某些键的某些值为null。我唯一正在玩的是spring boot文件上的application.properties。我在spring.jpa.hibernate.ddl-auto的“更新”和“无”之间进行切换。我做错了什么？

application.properties

spring.jpa.hibernate.format_sql=true
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver 
spring.datasource.url=jdbc:mysql://localhost:3306/riddlesgame
spring.datasource.username=root
spring.datasource.password=RiddlesGame886
spring.jpa.hibernate.ddl-auto=none
spring.jpa.show-sql=true
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL8Dialect
spring.data.rest.base-path=/api/v1
server.port=8088

这是数据库表和预期的列

这是返回的json，带有错误的null值

这是模特

@Entity
@Table(name = "allriddles")
public class Riddle {

/*
 * ATTRIBUTES
 */
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private int id;
private String title;
private int difficulty;
private String prize;
private String riddlerName;
private int levels;
private String riddleDescription;

/*
 * CONSTRUCTORS
 */
public Riddle() {}
public Riddle( String title, int difficulty, String prize, String riddlerName, int levels,
        String description) {
    super();
    
    this.title = title;
    this.difficulty = difficulty;
    this.prize = prize;
    this.riddlerName = riddlerName;
    this.levels = levels;
    this.riddleDescription = description;
}
}

这是我的呼叫服务的控制器

 @RestController
 public class GetRiddles {

@Autowired
RiddlesService rs; 


@RequestMapping("/Riddles")
public List<Riddle> getAllRiddles(){
    return rs.getAllRiddles();
}

所谓的服务

@Service
public class RiddlesService {

@Autowired
RiddlesRepository riddlesRepository;

public List<Riddle> getAllRiddles(){
    List<Riddle> riddles = new ArrayList<>();
    riddlesRepository.findAll()
    .forEach(riddles::add);
    

    return riddles;
}

原始界面

public interface RiddlesRepository extends CrudRepository<Riddle, Integer> {

}

最后是控制台输出，如果有帮助的话