So I ran `composer require restler/framework:3.0.0-RC5` and after
composer update the warnings disappeared.
BTW, I noticed that restler's Autoloader class has been modified in
dolibarr-developp : I ran `composer require
restler/framework:3.0.0-RC6` to restore the previous version and the
autoloading didn't work anymore, I had to copy the modified
Autoloader.php from dolibarr-developp