on 23 Apr 2018 the Jour Fixe accepted the list of supported software for ILIAS 5.4.x.
One decision was the support of PHP 7.2 due to the tightened release cycle of the PHP project. As you maybe already noticed in the latest pull requests there were and still are lots of PHP 7.2. issues in ILIAS 5.4.x resulting in run-time warnings (E_WARNING).
The major defect characteristics could be summarized as: - Counting non countable values  - Using undefined constants  - Using get_class() with non objects 
We hereby encourage you to check your components in regards of PHP 7.2 compatibility. We also highly recommend to use PHP 7.2 (and maybe 7.3) for your local 5.4.x and 6.0.x developer installations.
Best regards Michael Jansen
on behalf of the ILIAS e.V. and the Technical Board
 https://docu.ilias.de/goto_docu_wiki_wpage_5221_1357.html#ilPageTocA2130  https://docu.ilias.de/goto_docu_wiki_wpage_5047_1357.html  https://github.com/ILIAS-eLearning/ILIAS/pulls?utf8=%E2%9C%93&q=PHP+7.2  http://php.net/manual/en/migration72.incompatible.php#migration72.incompatib...  http://php.net/manual/en/migration72.incompatible.php#migration72.incompatib...  http://php.net/manual/en/migration72.incompatible.php#migration72.incompatib...