MediaWiki internal error.

Original exception: [14090b892a1e7ceef8a8afbc] /wiki/%D9%86%D9%82%D8%A7%D8%B4_%D8%A7%D9%84%D8%AA%D8%B5%D9%86%D9%8A%D9%81:%D9%88%D8%B1%D8%B4%D8%A7%D8%AA_%D9%85%D8%B9%D8%B3%D9%83%D8%B1_%D8%A7%D9%84%D8%AA%D8%B9%D8%A8%D9%8A%D8%B1_%D8%A7%D9%84%D8%B1%D9%82%D9%85%D9%8A_%D8%A7%D9%84%D8%B9%D8%B1%D8%A8%D9%8A_2017 MWUnknownContentModelException from line 201 of /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/content/ContentHandlerFactory.php: The content model 'flow-board' is not registered on this wiki.
See https://www.mediawiki.org/wiki/Content_handlers to find out which extensions handle this content model.
Backtrace:
#0 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/content/ContentHandlerFactory.php(266): MediaWiki\Content\ContentHandlerFactory->validateContentHandler()
#1 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/content/ContentHandlerFactory.php(189): MediaWiki\Content\ContentHandlerFactory->createContentHandlerFromHook()
#2 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/content/ContentHandlerFactory.php(97): MediaWiki\Content\ContentHandlerFactory->createForModelID()
#3 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/MediaWiki.php(428): MediaWiki\Content\ContentHandlerFactory->getContentHandler()
#4 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/MediaWiki.php(311): MediaWiki->initializeArticle()
#5 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/MediaWiki.php(940): MediaWiki->performRequest()
#6 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/MediaWiki.php(543): MediaWiki->main()
#7 /var/www/adef.xyz/wiki/mediawiki-1.35.1/index.php(53): MediaWiki->run()
#8 /var/www/adef.xyz/wiki/mediawiki-1.35.1/index.php(46): wfIndexMain()
#9 {main}

Exception caught inside exception handler: [14090b892a1e7ceef8a8afbc] /wiki/%D9%86%D9%82%D8%A7%D8%B4_%D8%A7%D9%84%D8%AA%D8%B5%D9%86%D9%8A%D9%81:%D9%88%D8%B1%D8%B4%D8%A7%D8%AA_%D9%85%D8%B9%D8%B3%D9%83%D8%B1_%D8%A7%D9%84%D8%AA%D8%B9%D8%A8%D9%8A%D8%B1_%D8%A7%D9%84%D8%B1%D9%82%D9%85%D9%8A_%D8%A7%D9%84%D8%B9%D8%B1%D8%A8%D9%8A_2017 MWUnknownContentModelException from line 201 of /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/content/ContentHandlerFactory.php: The content model 'flow-board' is not registered on this wiki.
See https://www.mediawiki.org/wiki/Content_handlers to find out which extensions handle this content model.
Backtrace:
#0 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/content/ContentHandlerFactory.php(266): MediaWiki\Content\ContentHandlerFactory->validateContentHandler()
#1 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/content/ContentHandlerFactory.php(189): MediaWiki\Content\ContentHandlerFactory->createContentHandlerFromHook()
#2 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/content/ContentHandlerFactory.php(97): MediaWiki\Content\ContentHandlerFactory->createForModelID()
#3 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/Title.php(4508): MediaWiki\Content\ContentHandlerFactory->getContentHandler()
#4 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/skins/SkinTemplate.php(176): Title->getPageViewLanguage()
#5 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/skins/SkinTemplate.php(373): SkinTemplate->wrapHTML()
#6 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/skins/SkinTemplate.php(127): SkinTemplate->prepareQuickTemplate()
#7 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/skins/SkinTemplate.php(144): SkinTemplate->generateHTML()
#8 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/OutputPage.php(2615): SkinTemplate->outputPage()
#9 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/exception/MWException.php(193): OutputPage->output()
#10 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/exception/MWException.php(231): MWException->reportHTML()
#11 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/exception/MWExceptionHandler.php(104): MWException->report()
#12 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/exception/MWExceptionHandler.php(185): MWExceptionHandler::report()
#13 /var/www/adef.xyz/wiki/mediawiki-1.35.1/includes/MediaWiki.php(576): MWExceptionHandler::handleException()
#14 /var/www/adef.xyz/wiki/mediawiki-1.35.1/index.php(53): MediaWiki->run()
#15 /var/www/adef.xyz/wiki/mediawiki-1.35.1/index.php(46): wfIndexMain()
#16 {main}