Serialization of 'Closure' is not allowed

[str]

Steps to reproduce:

1. git submodule add https://github.com/phly/PhlyContact.git vendor/PhlyContact
2. added "zendframework/zendservice-recaptcha": "2.*" to composer.json
3. composer update
4. cp vendor/PhlyContact/config/module.phly-contact.local.php config/autoload/module.phly-contact.local.php
5. set the recaptcha priv/pub keys, message from/to/address and mail_transporte auth in the config file
6. load /contact page

Got the following error message:

An error occurred during execution; please try again later.
/var/www/vendor/zendframework/zendframework/library/Zend/Stdlib/PriorityQueue.php:178

Message:   Serialization of 'Closure' is not allowed

Stack trace:
#0 /var/www/vendor/zendframework/zendframework/library/Zend/Stdlib/PriorityQueue.php(178): serialize(Array)
#1 [internal function]: Zend\Stdlib\PriorityQueue->serialize()
#2 /var/www/vendor/zendframework/zendframework/library/Zend/Stdlib/ArrayObject.php(333): serialize(Array)
#3 /var/www/vendor/PhlyContact/view/phly-contact/contact/index.phtml(24): Zend\Stdlib\ArrayObject->serialize()
#4 /var/www/vendor/PhlyContact/view/phly-contact/contact/index.phtml(24): Zend\Form\View\Helper\Form->openTag(Object(PhlyContact\Form\ContactForm))
#5 /var/www/vendor/zendframework/zendframework/library/Zend/View/Renderer/PhpRenderer.php(506): include('/home/str/publi...')
#6 /var/www/vendor/zendframework/zendframework/library/Zend/View/View.php(205): Zend\View\Renderer\PhpRenderer->render(Object(Zend\View\Model\ViewModel))
#7 /var/www/vendor/zendframework/zendframework/library/Zend/View/View.php(233): Zend\View\View->render(Object(Zend\View\Model\ViewModel))
#8 /var/www/vendor/zendframework/zendframework/library/Zend/View/View.php(198): Zend\View\View->renderChildren(Object(Zend\View\Model\ViewModel))
#9 /var/www/vendor/zendframework/zendframework/library/Zend/Mvc/View/Http/DefaultRenderingStrategy.php(103): Zend\View\View->render(Object(Zend\View\Model\ViewModel))
#10 [internal function]: Zend\Mvc\View\Http\DefaultRenderingStrategy->render(Object(Zend\Mvc\MvcEvent))
#11 /var/www/vendor/zendframework/zendframework/library/Zend/EventManager/EventManager.php(468): call_user_func(Array, Object(Zend\Mvc\MvcEvent))
#12 /var/www/vendor/zendframework/zendframework/library/Zend/EventManager/EventManager.php(207): Zend\EventManager\EventManager->triggerListeners('render', Object(Zend\Mvc\MvcEvent), Array)
#13 /var/www/vendor/zendframework/zendframework/library/Zend/Mvc/Application.php(352): Zend\EventManager\EventManager->trigger('render', Object(Zend\Mvc\MvcEvent))
#14 /var/www/vendor/zendframework/zendframework/library/Zend/Mvc/Application.php(327): Zend\Mvc\Application->completeRequest(Object(Zend\Mvc\MvcEvent))
#15 /var/www/public/index.php(35): Zend\Mvc\Application->run()
#16 {main}