<?php
use DI\ContainerBuilder;

require 'vendor/autoload.php';

$builder = new ContainerBuilder();
$container = $builder->build();

$test = function($optional = 'default') {
    echo $optional;
};

$container->call($test);

output version 4.4.10: default

output version 5: Fatal error: Uncaught exception 'Invoker\Exception\NotEnoughParametersException' with message 'Unable to invoke the callable because no value was given for parameter 1 ($optional)'