Person with partner relationship

Person.java

@Entity
@Data
public class Person extends core.Person {
    @OneToOne(fetch = LAZY)
    private Person wife;

    @OneToOne(fetch = LAZY, mappedBy = "wife")
    private Person husband;

    public Person getPartner() {
        if ((wife != null) && (husband != null)) throw new IllegalStateException();

        if (wife != null) return wife;

        if (husband != null) return husband;

        return null;
    }
}