Hexadecimal string with odd number of characters

@Repository
public class GifDAOImpl implements GifDao{
    @Autowired
    private SessionFactory sessionFactory;

    @Override
    public List<Gif> findAll() {
        Session session = sessionFactory.openSession();
        CriteriaBuilder builder = session.getCriteriaBuilder();
        CriteriaQuery<Gif> criteria = builder.createQuery(Gif.class);
        criteria.from(Gif.class);
        List<Gif> gifs = session.createQuery(criteria).getResultList();
        session.close();
        return gifs;
    }

    @Override
    public Gif findById(Long id) {
        Session session = sessionFactory.openSession();
        Gif gif = session.get(Gif.class,id);
        session.close();
        return gif;
    }

    @Override
    public void save(Gif gif) {
        Session session = sessionFactory.openSession();
        session.beginTransaction();
        session.save(gif);
        session.getTransaction().commit();
        session.close();
    }

@Service
public class GifServiceImpl implements GifService {
    @Autowired
    private GifDao gifDao;

    @Override
    public List<Gif> findAll() {
        return gifDao.findAll();
    }

    @Override
    public Gif findById(Long id) {
        return gifDao.findById(id);
    }

    @Override
    public void save(Gif gif, MultipartFile file) {
        try {
            gif.setBytes(file.getBytes());
            gifDao.save(gif);
        } catch (IOException e) {
            System.err.println("Unable to get byte array from uploaded file.");
        }
    }

    // Single GIF page
    @RequestMapping("/gifs/{gifId}")
    public String gifDetails(@PathVariable Long gifId, Model model) {
        // TODO: Get gif whose id is gifId
        Gif gif = gifService.findById(gifId);

        model.addAttribute("gif", gif);
        return "gif/details";
    }

    // GIF image data
    @RequestMapping("/gifs/{gifId}.gif")
    @ResponseBody
    public byte[] gifImage(@PathVariable Long gifId) {
        // TODO: Return image data as byte array of the GIF whose id is gifId
        return gifService.findById(gifId).getBytes();
    }

    // Upload a new GIF
    @RequestMapping(value = "/gifs", method = RequestMethod.POST)
    public String addGif(@RequestParam MultipartFile file, Gif gif, RedirectAttributes attributes) {
        // TODO: Upload new GIF if data is valid
        gifService.save(gif, file);
        attributes.addFlashAttribute("flash",new FlashMessage("GIF successfully uploaded", FlashMessage.Status.SUCCESS));

        // TODO: Redirect browser to new GIF's detail view
        return String.format("redirect:/gifs/%s",gif.getId());
    }