не понимаю, где ошибка

public static ByteArrayOutputStream serializeSingletonInstance(Singleton instance) throws IOException {
        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();

        ObjectOutputStream oos = new ObjectOutputStream(byteArrayOutputStream);
        oos.writeObject(instance);
        oos.close();

        return byteArrayOutputStream;
    }

    public static Singleton deserializeSingletonInstance(ByteArrayOutputStream byteArrayOutputStream) throws IOException, ClassNotFoundException {
        ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(byteArrayOutputStream.toByteArray());

        ObjectInputStream ois = new ObjectInputStream(byteArrayInputStream);
        Singleton singleton = (Singleton) ois.readObject();
        singleton.readResolve();
        ois.close();

        return singleton;
    }

    public static class Singleton implements Serializable {
        private static Singleton ourInstance;

        public static Singleton getInstance() {
            if (ourInstance == null) {
                ourInstance = new Singleton();
            }
            return ourInstance;
        }

        private Singleton() {
        }

        private static Object readResolve() {
            return ourInstance;
        }
    }