How to save images in cakephp 3.4.0 with cakephp-upload while being immutable


I’m working on my cakephp project
and I am currently upgrading from 3.3.16 to 3.4.0

The project uses the cakephp-upload plugin to save an image.
The Upload plugin needs an existing entity to attach a file to it. A modification of the request is done to grab the avatar, before unsetting it to save the user.

I know this is not a good practice to modify a request, but the code was made this way.
With immutable objects in version 3.4.0, it is just not possible anymore. But i dont know how to do it properly.

Here is the error message given by my unit-test,
ran by vendor/bin/phpunit --filter testAdd tests/TestCase/Controller/Api/V1/UsersControllerTest.php:

There was 1 failure:

1) App\Test\TestCase\Controller\Api\V1\UsersControllerTest::testAdd
Failed asserting that file "/home/comptoir/Comptoir-srv/webroot/img/files/Users/photo/5/avatar/correctAvatarLogo.jpg" exists.


Here is the actual code:

public function add()
        if (!empty($this->request->data)) {
            $user = $this->Users->newEntity($this->request->data);
        } else {
            $user = $this->Users->newEntity();

        $message = "";
        // Get the avatar before unset it to save the user.
        // The Upload plugin need an existing entity to attach a file to it.

        if ($this->request->is('post')) {
            if (isset($this->request->data['photo']) && !$user->errors()) {
                $avatar = $this->request->data['photo'];
                $this->request->data['photo'] = "";

            $user = $this->Users->patchEntity($user, $this->request->data);

            if ($this->Users->save($user)) {
                $user = $this->Users->get($user->id, ['contain' => []]);

                isset($avatar) ? $this->request->data['photo'] = $avatar : null;

                $user = $this->Users->patchEntity($user, $this->request->data);

                if ($this->Users->save($user)) {
                    $message = "Success";
                    $this->Flash->success(__d("Forms", "Your are registred on the Comptoir du Libre, welcome !"));
                    if (!$this->request->is('json')) {
                            "prefix" => false,
                            "controller" => "Pages",
                            "language" => $this->request->param("language")
                } else {
                    $message = "Error";
            } else {
                $message = "Error";
                $this->Flash->error(__d("Forms", "Your registration failed, please follow rules in red."));

            $message == "Error" ? $this->set('errors', $user->errors()) : null;

        $this->ValidationRules->config('tableRegistry', "Users");
        $rules = $this->ValidationRules->get();
        $userTypes = $this->Users->UserTypes->find('list', ['limit' => 200]);
        $this->set(compact('user', 'userTypes', 'rules', 'message'));
        $this->set('_serialize', ['user', 'userTypes', 'rules', 'message', 'errors']);

Does anyone know how to do that respecting the immutable rule ?

This would be converted to

if (isset($this->request->getData('photo')) && !$user->errors()) {
    $avatar = $this->request->getData('photo');
    $this->request = $this->request->withData('photo', '');