preg_replace(): Unknown modifier ']'

[nvirth]

Executing these:

use Stringy\Stringy;

$text = Stringy::create('/asd/qwe/');
$text = $text->trim(' \\/');

(A)

With mbstring extension enabled in php.ini
=> It works fine, result is 'asd/qwe'

(B)

Without mbstring
=> It is buggy, result is '', and there is a php warning: preg_replace(): Unknown modifier ']'