MediaWiki internal error.

Original exception: [acf035de0b700b327faa1ca1] /index.php?title=Newsletter:Datencockpit&oldid=3696 MWUnknownContentModelException: The content model 'NewsletterContent' is not registered on this wiki.
See https://www.mediawiki.org/wiki/Content_handlers to find out which extensions handle this content model.
Backtrace:
from /home/datencockpit/public_html/includes/content/ContentHandlerFactory.php(203)
#0 /home/datencockpit/public_html/includes/content/ContentHandlerFactory.php(273): MediaWiki\Content\ContentHandlerFactory->validateContentHandler()
#1 /home/datencockpit/public_html/includes/content/ContentHandlerFactory.php(191): MediaWiki\Content\ContentHandlerFactory->createContentHandlerFromHook()
#2 /home/datencockpit/public_html/includes/content/ContentHandlerFactory.php(97): MediaWiki\Content\ContentHandlerFactory->createForModelID()
#3 /home/datencockpit/public_html/includes/page/WikiPage.php(296): MediaWiki\Content\ContentHandlerFactory->getContentHandler()
#4 /home/datencockpit/public_html/includes/MediaWiki.php(437): WikiPage->getContentHandler()
#5 /home/datencockpit/public_html/includes/MediaWiki.php(320): MediaWiki->initializeArticle()
#6 /home/datencockpit/public_html/includes/MediaWiki.php(904): MediaWiki->performRequest()
#7 /home/datencockpit/public_html/includes/MediaWiki.php(562): MediaWiki->main()
#8 /home/datencockpit/public_html/index.php(50): MediaWiki->run()
#9 /home/datencockpit/public_html/index.php(46): wfIndexMain()
#10 {main}

Exception caught inside exception handler: [acf035de0b700b327faa1ca1] /index.php?title=Newsletter:Datencockpit&oldid=3696 MWUnknownContentModelException: The content model 'NewsletterContent' is not registered on this wiki.
See https://www.mediawiki.org/wiki/Content_handlers to find out which extensions handle this content model.
Backtrace:
from /home/datencockpit/public_html/includes/content/ContentHandlerFactory.php(203)
#0 /home/datencockpit/public_html/includes/content/ContentHandlerFactory.php(273): MediaWiki\Content\ContentHandlerFactory->validateContentHandler()
#1 /home/datencockpit/public_html/includes/content/ContentHandlerFactory.php(191): MediaWiki\Content\ContentHandlerFactory->createContentHandlerFromHook()
#2 /home/datencockpit/public_html/includes/content/ContentHandlerFactory.php(97): MediaWiki\Content\ContentHandlerFactory->createForModelID()
#3 /home/datencockpit/public_html/includes/page/WikiPage.php(296): MediaWiki\Content\ContentHandlerFactory->getContentHandler()
#4 /home/datencockpit/public_html/includes/page/WikiPage.php(282): WikiPage->getContentHandler()
#5 /home/datencockpit/public_html/includes/page/Article.php(2071): WikiPage->getActionOverrides()
#6 /home/datencockpit/public_html/includes/actions/ActionFactory.php(264): Article->getActionOverrides()
#7 /home/datencockpit/public_html/includes/actions/ActionFactory.php(364): MediaWiki\Actions\ActionFactory->getAction()
#8 /home/datencockpit/public_html/includes/actions/Action.php(112): MediaWiki\Actions\ActionFactory->getActionName()
#9 /home/datencockpit/public_html/extensions/CommentStreams/includes/CommentStreamsHandler.php(212): Action::getActionName()
#10 /home/datencockpit/public_html/extensions/CommentStreams/includes/CommentStreamsHandler.php(192): MediaWiki\Extension\CommentStreams\CommentStreamsHandler->checkDisplayComments()
#11 /home/datencockpit/public_html/extensions/CommentStreams/includes/MainHooks.php(275): MediaWiki\Extension\CommentStreams\CommentStreamsHandler->init()
#12 /home/datencockpit/public_html/includes/HookContainer/HookContainer.php(160): MediaWiki\Extension\CommentStreams\MainHooks->onBeforePageDisplay()
#13 /home/datencockpit/public_html/includes/HookContainer/HookRunner.php(945): MediaWiki\HookContainer\HookContainer->run()
#14 /home/datencockpit/public_html/includes/OutputPage.php(2871): MediaWiki\HookContainer\HookRunner->onBeforePageDisplay()
#15 /home/datencockpit/public_html/includes/exception/MWException.php(181): OutputPage->output()
#16 /home/datencockpit/public_html/includes/exception/MWException.php(215): MWException->reportHTML()
#17 /home/datencockpit/public_html/includes/exception/MWExceptionHandler.php(129): MWException->report()
#18 /home/datencockpit/public_html/includes/exception/MWExceptionHandler.php(248): MWExceptionHandler::report()
#19 /home/datencockpit/public_html/includes/MediaWiki.php(581): MWExceptionHandler::handleException()
#20 /home/datencockpit/public_html/index.php(50): MediaWiki->run()
#21 /home/datencockpit/public_html/index.php(46): wfIndexMain()
#22 {main}