Cannot read property 'length' of null

i'm new with jlexart youtube feedpro but get it not working on this Joomla site


it's keep shwoing the loading symbol


The browser inspections shows error


Uncaught TypeError: Cannot read property 'length' of null
    at YTF._this.getData (script.js?v=5.1.2:1124)
    at new YTF (script.js?v=5.1.2:1567)
    at HTMLDocument. (videos-2.html:158)
    at u (jquery.min.js?53ccc10cee0db4dc32475054232f7f08:2)
    at Object.add [as done] (jquery.min.js?53ccc10cee0db4dc32475054232f7f08:2)
    at a.fn.init.d.fn.ready (jquery.min.js?53ccc10cee0db4dc32475054232f7f08:2)
    at videos-2.html:157
    at videos-2.html:160


https://www.hervormdberkel.nl/kijken-luisteren-en-lezen/kijken/videos-2.html

kind regards
Paul