Symfony version(s) affected: 5.0.4 and 4.4.4 and maybe others.

Description
When i use '/' or ['/'] as parametr in method Finder::in, got exception during iteration: Directory name must not be empty. In line 48 /vendor/symfony/finder/Iterator/RecursiveDirectoryIterator.php.

How to reproduce
(code should works of unix like systems)

use Symfony\Component\Finder\Finder;

$finder = new Finder();
$finder->in('/');
foreach($finder as $item){
}