How can i add oneToMany mapping with inheritence SINGLE_TABLE

Question

I'm using inheritence with JPA and HIBERNATE so i have these entities :

@Entity
@Inheritance( strategy = InheritanceType.SINGLE_TABLE )
@DiscriminatorColumn( name = "entityType", 
        discriminatorType = DiscriminatorType.STRING )
public abstract class A implements Serializable
{
    @Id
    private String id;
    @ManyToOne
    @JoinColumn(name = "Z_ID", nullable = false)
    private Z z;

    // other mapped properties...
}

@Entity
@DiscriminatorValue("BB")
public class BB extends A
{
    @Basic( optional = false)
    @Column( table = "BB" )
    private String property1;

    // other mapped properties and associations...
}

@Entity
@DiscriminatorValue("CC")
public class CC extends A
{
    @ManyToOne( optional = false)
    @JoinColumn( table = "CC" )
    private SomeEntity association1;

    // other mapped properties and associations...
}
public class Z implements Serializable
{
    @Id
    private String id;
    @OneToMany(fetch = FetchType.LAZY, mappedBy = "z", cascade= CascadeType.ALL, orphanRemoval=true)
    private Set<A> as;

    // other mapped properties...
}

I know that i can add two attributes bb and cc in the entity Z but have many other entities inheritence from A so i ask if there any solution to only one attribute z. The implementation above gave me an exception :

org.hibernate.exception.GenericJDBCException: Could not read entity state from ResultSet

This is the hole exception as images