Beta 1 - Error 500 if there is a Twitter widget on page

After upgrading from latest 4.x version, I got the following error on these pages where a Twitter Widget is displayed:

 AH01071: Got error 'PHP message: PHP Fatal error:  Declaration of IPS\\core\\widgets\\_twitter::configuration(&$form = null) must be compatible with IPS\\Widget::configuration(?IPS\\Helpers\\Form &$form = null): IPS\\Helpers\\Form in /var/www/html/applications/core/widgets/twitter.php on line 47'