Type error in SYSTEMPATH\View\Cells\Cell.php at line 88

I got a type error in SYSTEMPATH\View\Cells\Cell.php at line 88:
substr(): Argument #3 ($length) must be of type ?int, bool given
because of
declare(strict_types=1);
I changed the code to:
            $pos = strrpos($viewName, '_cell');
            if ($pos === false) {
              $possibleView1 = $directory . $viewName . '.php';             
            } else {
              $possibleView1 = $directory . substr($viewName, 0, $pos) . '.php';
            }

Now the gallery using Cell.php is working. I hope it helps.