Fatal error on DateTimeImmutable::createFromMutable

[tjveldhuizen]

root@19da4cbeb2d9:/app/src# php -v
PHP 8.0.8 (cli) (built: Jul  1 2021 22:40:15) ( NTS )
Copyright (c) The PHP Group
Zend Engine v4.0.8, Copyright (c) Zend Technologies
    with Zend OPcache v8.0.8, Copyright (c), by Zend Technologies
    with Xdebug v3.1.0beta2, Copyright (c) 2002-2021, by Derick Rethans

<?php
require('../vendor/autoload.php');

$date = new \DateTime();
$immutable = \Safe\DateTimeImmutable::createFromMutable($date);

results in:

Fatal error: Uncaught Error: Call to a member function format() on null in /app/vendor/thecodingmachine/safe8/lib/DateTimeImmutable.php:75
Stack trace:
#0 /app/vendor/thecodingmachine/safe8/lib/DateTimeImmutable.php(38): Safe\DateTimeImmutable->format('Y-m-d H:i:s.u')
#1 /app/vendor/thecodingmachine/safe8/lib/DateTimeImmutable.php(241): Safe\DateTimeImmutable::createFromRegular(Object(Safe\DateTimeImmutable))
#2 /app/src/test.php(5): Safe\DateTimeImmutable::createFromMutable(Object(DateTime))
#3 {main}
  thrown in /app/vendor/thecodingmachine/safe8/lib/DateTimeImmutable.php on line 75