short information about the system:
XWiki Debian 12.5.1 on Ubuntu 18.04 LTS with tomcat9 and mysql.
Installed with the help of this manual https://www.xwiki.org/xwiki/bin/view/Documentation/AdminGuide/Installation/InstallationViaAPT/
After setting up all necesary things (most of the time LDAPs), i imported the articles from an old XWiki instance, ok, the old instance is nearly same system with XWiki 12.3, but an upgrade always fails, so i decided to go this way.
Now if i open an article i get following errors in the Log at each time someone opens an article:
Jul 28 16:04:02 <servername> tomcat9: 2020-07-28 16:04:02,448 [http-nio-8080-exec-22 - <Article-URL>] ERROR o.a.v.rendering - Left side ($unlicensedSheets.size()) of comparison operation has null value at xwiki:Licenses.Code.MissingLicensesUIX^XWiki.UIExtensionClass[line 5, column 61]
This error even occours on complete new created empty sites in the new wiki.
I almost forgot, there is no paid extension installed in the system.
If you need further informations feel free to ask.
Thanks for any help.