TypeError: count(): Argument #1 ($value) must be of type Countable|array, null given

An unforeseen error has occured. This is most likely a bug somewhere. It might be a problem in the dw2pdf plugin.

/srv/www/iqwiki.iqo.uni-hannover.de/lib/plugins/dw2pdf/vendor/mpdf/mpdf/src/Otl.php:279