Is it correct to modify object inside reactive flow, when it was defined outside of it?
Example:

public Single<MyDto> createDto() {
    MyDto dto = new MyDto();
    return Single.just(“testUserName”)
      .flatmap(userName -> return userService.findUserById(userName)
         .map(user->{
                 dto.setId(user.getId());
                 return dto;
          });
      )
  };
    

UserService does rest call to get User and returns Single <User>.
Can there be a case when I would get myDto with empty ‘id’ field?