Warnings in RSS Importer

I’m using RSS Importer in my website and I get the following:

Warning: getimagesize(https://www.wprost.pl/F/pic.php?w140=1&T=news&P=309932): failed to open stream: no suitable wrapper could be found in /home/mhd-01/www.turkawka.com/htdocs/wp/wordpress/wp-content/plugins/wp-rss-retriever/wp-rss-retriever.php on line 155

Any ideas of the problem?

https://www.ads-software.com/plugins/rss-importer/