Jhipster Issue with updateUser

Question

public Optional<UserDTO> updateUser(UserDTO userDTO) {
        return Optional.of(userRepository
            .findOne(userDTO.getId()))
            .map(user -> {
                user.setLogin(userDTO.getLogin());
                user.setFirstName(userDTO.getFirstName());
                user.setLastName(userDTO.getLastName());
                user.setEmail(userDTO.getEmail());
                user.setImageUrl(userDTO.getImageUrl());
                user.setActivated(userDTO.isActivated());
                user.setLangKey(userDTO.getLangKey());
                Set<Authority> managedAuthorities = user.getAuthorities();
                managedAuthorities.clear();
                userDTO.getAuthorities().stream()
                    .map(authorityRepository::findOne)
                    .forEach(managedAuthorities::add);
                cacheManager.getCache(UserRepository.USERS_BY_LOGIN_CACHE).evict(user.getLogin());
                cacheManager.getCache(UserRepository.USERS_BY_EMAIL_CACHE).evict(user.getEmail());
                log.debug("Changed Information for User: {}", user);
                return user;
            })
            .map(UserDTO::new);
    }

I have a problem with the function Optional<UserDTO> updateUser(UserDTO userDTO)

There is no userRepository.save(user); but the save is successful.

How should I understand where this is saved？！