Invalid format for createdBy in SpringBoot Auditable

Question

I implemented SpringBoot Auditable and everything is working fine except the createdBy is giving timestamp.

Here is my Auditable class:

@Getter
@Setter
public class Auditable {

    @CreatedDate
    private LocalDateTime createdAt;

    @LastModifiedDate
    private LocalDateTime updatedAt;

    @CreatedBy
    private ObjectId createdBy;

    @LastModifiedBy
    private ObjectId updatedBy;

}

And here is my AuditorAwareImpl class:

public class AuditorAwareImpl implements AuditorAware<ObjectId> {

    @Override
    public Optional<ObjectId> getCurrentAuditor() {

        Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
        ObjectId userId = null;
        if (authentication != null) {
            UserDetails userDetails = (UserDetails) authentication.getPrincipal();

            userId = new ObjectId(userDetails.getId());
        }
        return Optional.of(userId);
    }
}

It's(ObjectId) saving fine to DB. But when I retrieve that record, I'm getting createdBy as different format instead of ObjectId:

Can someone help me with this please?