PHP warning related to a missing file from the Twig library

Overview of the issue

In the 3.5.2 version of WPML, some files related to the Twig library and used by the plugin, are missing.

This may produce a PHP warning on some pages, similar to this one:

PHP Warning:  include(/var/www/example.com/wp-content/plugins/sitepress-multilingual-cms/embedded/twig/twig/lib/Twig/Node/Expression/Test/Defined.php): failed to open stream: No such file or directory in /var/www/example.com/wp-content/plugins/sitepress-multilingual-cms/embedded/composer/ClassLoader.php on line 412

Workaround

We updated the release archive so that it includes the missing files.

A proper action if you encounter this problem is to re-download WPML.