What is wrong with the following Spring Boot code snippet?

What is wrong with the following Spring Boot code snippet?

@Service
public class UserService {
    private Repository repo;

    @Autowired
    public void setRepo(Repository repo) {
        this.repo = repo;
    }
}

@RestController
public class UserController {
    @Autowired
    private UserService userService;

    public void doSomething() {
        userService.repo.save();
    }
}