我试图建模一个一对多的关系，其中外键是复合键的一部分。不幸的是，我遇到了以下错误消息：
第一个月
我的实体如下：

@Entity
@Table(name = "point_in_time")
class PointInTime(
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    var id: Long,
    val title: String,
    val note: String,
    @OneToMany(mappedBy = "symptom")
    val symptoms: Set<Symptom>
) {
    @field:Column(updatable = false)
    val createdAt: Instant = Instant.now()
}

@Entity
@Table(name = "symptom")
@IdClass(SymptomId::class)
class Symptom(
    @ManyToOne(optional = false)
    @Id
    @JoinColumn(name = "point_in_time_id", nullable = false)
    val pointInTime: PointInTime,
    @Id
    val category: String,
    @Id
    val symptom: String,
    val strength: Strength
)

class SymptomId (
    val pointInTime: Long,
    val category: String,
    val symptom: String
): Serializable

这个异常的原因是什么，我如何避免它？