The Symfony\Bundle\TwigBundle\Loader\FilesystemLoader::exists() method throws a deprecated exception:

In Symfony\Bundle\TwigBundle\Loader\FilesystemLoader::findTemplate(), you must accept a second argument that when set to "false" returns "false" instead of throwing an exception. Not supporting this argument is deprecated since version 1.27

In Symfony\Bundle\TwigBundle\Loader\FilesystemLoader::findTemplate(), the $throw argument isn't passed to the Twig_Loader_Filesystem::findTemplate() parent method.

The result, is that the value of func_num_args() is equal to 1 and not the value 2.