为什么hibernate要求java.lang.Double的默认构造函数？

我使用JPA和Hibernate作为提供程序，我想用@ElementCollection映射 Map<Embeddable, Double> ，但是当持久化时，我得到了一个hibernate异常：

javax.persistence.PersistenceException: org.hibernate.InstantiationException: No default constructor for entity: java.lang.Double

我知道 ：

如果Map的值是可嵌入的或基本类型，则Map将映射为元素集合 . [Pro JPA 2 Second edition- Page 102]

所以在我的情况下我应该使用@ElementCollection，但为什么hibernate认为Double是一个实体并要求一个默认的构造函数？

Hibernate / JPA依赖项：

<properties>        
        <hibernate.version>5.2.10.Final</hibernate.version>
    </properties>

    <dependencies>

        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>${hibernate.version}</version>
        </dependency>
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-entitymanager</artifactId>
            <version>${hibernate.version}</version>
        </dependency>
        <dependency>
            <groupId>org.hibernate.javax.persistence</groupId>
            <artifactId>hibernate-jpa-2.1-api</artifactId>
            <version>1.0.0.Final</version>
        </dependency>
  ....
  <dependencies>

我的类（我使用具有继承单表策略的泛型类型）：

@Entity
@Table(name = "GENERIC_STAFF")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "My_Discriminator", discriminatorType = DiscriminatorType.STRING, length = 255)
public class FirstLevelBaseClass {  

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO) 
    private Long id;

    public Long getId() {
        return id;
    }   
}

 @Getter @Setter
 public class SecondLevelBaseClass <K extends Serializable, V extends Serializable, M extends Map<K, V>> extends FirstLevelBaseClass{
     private M value;
 }

@Entity // Class that I want to persist
@DiscriminatorValue(value = "My_DoubleMapClass")
@Access(AccessType.PROPERTY)
public class DoubleMapClass extends SecondLevelBaseClass<EmbeddableDate, Double, SortedMap<EmbeddableDate, Double>>{

    @Override
    @ElementCollection
    @CollectionTable(joinColumns = @JoinColumn(name = "ID_GENERIC"))
    @AttributeOverrides({
        @AttributeOverride(name = "key.start", column = @Column(name = "START")),
        @AttributeOverride(name = "key.end", column = @Column(name = "END"))
    })
    @Column(nullable = false, name = "MyValue")
    @OrderBy    
    public SortedMap<EmbeddableDate, Double> getValue() {
        return super.getValue();
    }

    @Override
    public void setValue(SortedMap<EmbeddableDate, Double> value) {
        super.setValue(value);
    }
}