Nested Unidirectional OnetoMany with Mapstruct Mapper interface returning null for the second level DTO class with

Question

I have 4 classes with Unidirectional @OneToMany relationship as below:

Class A {
  // some properties
  List<B> bList = new ArrayList<>();
}

Class B has a Set of Class C

Class B {
   // Some properties
   Set<C> cSet = new HashSet<>();
}

Class C has a One to One relationship with Class D

Class C {
   // Some properties here
   D d;
}

AMapper interface looks below;

@Mapper(componentModel="spring", uses= {BMapper.class})
public interface AMapper {

    @Mapping(target = "aId", source="id")
    ADTO toDTO(final A a);

    @Mapping(target = "id", ignore = true)
    A toEntity(final ADTO aDTO);

}

BMapper as below:

@Mapper(componentModel="spring", uses= {CMapper.class})
public interface BMapper {
    @Mapping(target = "bId", source="id")
    @Mapping(target = "xxx", ignore = true)
    @Mapping(target = "yyy", ignore = true)
    BDTO toDTO(final BData entity);

    @Mapping(target = "id", ignore = true)
    B toEntity(final BDTO dto);

    Iterable<B> bDtoToBListEntity(Iterable<BDTO> list);

    Iterable<BDTO> bListEntityToBDto(Iterable<B> list);
 
    
 
}

CMapper as below

@Mapper(componentModel = "spring", uses = { DMapper.class })
public interface CMapper {
    CDTO toDTO(C c);

    @Mapping(target = "id", ignore = true)
    C toEntity(CDTO planet);

    Set<C> cDtoToCSetEntity(Set<CDTO> set);

    Set<CDTO> cSetEntityToCDto(Set<C> set);
}
    

DMapper as below:

@Mapper(componentModel = "spring")
public interface DMapper {
    DDTO toDTO(D d);

    D toEntity(DDTO d);
}

@Service
AService {
    public ADTO get(final Long id) {
        return aMapper.toDTO( findById(id));
    }
}

What is the problem? I am able to successfully read the bList when through the service class's get method however, cSet from class B is empty (not null though). Should I manually read the bDTO to populate the cSet? I hope not as I assume that's where the mapstruct is helping us. Any idea what is that I am missing? Thanks.