class Request {
    Nullable<ChildRequest> child;
}

class ChildRequest {
    String name;
}

class RequestDto {
    JsonNullable<ChildRequestDto> child;
}

class ChildRequestDto {
    String name;
}

@Mapper
public interface RequestMapper {

    RequestMapper INSTANCE = Mappers.getMapper( RequestMapper.class );

    Request map(RequestDto dto);

    default <T> Nullable<T> jsonNullableToNullable(JsonNullable<T> jsonNullable) {
        if ( jsonNullable.isPresent() ) {
            return Nullable.of( jsonNullable.get() );
        }
        return Nullable.undefined();
    }

    default JsonNullable<ChildRequest> mapJsonNullableChildren(JsonNullable<ChildRequestDto> dtos) {
        if (dtos.isPresent()) {
            return JsonNullable.of( mapChild( dtos.get() ) );
        } else {
            return JsonNullable.undefined();
        }
    }

    ChildRequest mapChild(ChildRequestDto dto);
}