listener.php

<?php
class SessionCleanerListener implements Kdyby\Events\Subscriber
{
  
  private $session;
  
  public function __construct(Nette\Http\Session $session)
  {
    $this->session = $session;
  }
  
  public function getSubscribedEvents()
  {
    return ['Nette\Application\Application::onRequest'];
  }
  
  public function onRequest(Nette\Application\Application $app, Nette\Application\Request $request) 
  {
    if ($request->getPresenterName() === 'Foo' && $request->getParameter('action') === 'create') {
      return;
    }
    $this->session->getSection('xyzData')->foo = NULL;
  }
}