Uncaught TYPO3 Exception if the target of a external link is _top or _self

[Patta]

If the target value of a external link is _top or _self a uncaught TYPO3 exception error is shown.

Core: Exception handler (WEB): Uncaught TYPO3 Exception: Return value of GeorgRinger\Noopener\Hooks\LinkHook::checkSysDomains() must be of the type bool, null returned | TypeError thrown in file /var/www/vhosts/###REMOVED###/private/typo3conf/ext/noopener/Classes/Hooks/LinkHook.php in line 150. Requested URL: ###REMOVED###

Why _top or _self on a external link?
We host a url shortener and link to a shorten url which redirect to the same domain and don't need a new tab.

TYPO3 8.7.27
PHP 7.3.7
Composer mode
noopener dev-master

Thanks for this must-have extension.

[Patta]

fixed with 56e37f5