MediaWiki internal error.

Original exception: [941e5b24324646bfda3261eb] /wiki/Coasterpedia:Discussion MWUnknownContentModelException: 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:
from /var/lib/mediawiki/w/includes/content/ContentHandlerFactory.php(192)
#0 /var/lib/mediawiki/w/includes/content/ContentHandlerFactory.php(247): MediaWiki\Content\ContentHandlerFactory->validateContentHandler()
#1 /var/lib/mediawiki/w/includes/content/ContentHandlerFactory.php(181): MediaWiki\Content\ContentHandlerFactory->createContentHandlerFromHook()
#2 /var/lib/mediawiki/w/includes/content/ContentHandlerFactory.php(93): MediaWiki\Content\ContentHandlerFactory->createForModelID()
#3 /var/lib/mediawiki/w/includes/page/WikiPage.php(251): MediaWiki\Content\ContentHandlerFactory->getContentHandler()
#4 /var/lib/mediawiki/w/includes/MediaWiki.php(480): WikiPage->getContentHandler()
#5 /var/lib/mediawiki/w/includes/MediaWiki.php(361): MediaWiki->initializeArticle()
#6 /var/lib/mediawiki/w/includes/MediaWiki.php(960): MediaWiki->performRequest()
#7 /var/lib/mediawiki/w/includes/MediaWiki.php(613): MediaWiki->main()
#8 /var/lib/mediawiki/w/index.php(50): MediaWiki->run()
#9 /var/lib/mediawiki/w/index.php(46): wfIndexMain()
#10 {main}

Exception caught inside exception handler: [941e5b24324646bfda3261eb] /wiki/Coasterpedia:Discussion MWUnknownContentModelException: 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:
from /var/lib/mediawiki/w/includes/content/ContentHandlerFactory.php(192)
#0 /var/lib/mediawiki/w/includes/content/ContentHandlerFactory.php(247): MediaWiki\Content\ContentHandlerFactory->validateContentHandler()
#1 /var/lib/mediawiki/w/includes/content/ContentHandlerFactory.php(181): MediaWiki\Content\ContentHandlerFactory->createContentHandlerFromHook()
#2 /var/lib/mediawiki/w/includes/content/ContentHandlerFactory.php(93): MediaWiki\Content\ContentHandlerFactory->createForModelID()
#3 /var/lib/mediawiki/w/includes/page/WikiPage.php(251): MediaWiki\Content\ContentHandlerFactory->getContentHandler()
#4 /var/lib/mediawiki/w/includes/page/WikiPage.php(237): WikiPage->getContentHandler()
#5 /var/lib/mediawiki/w/includes/page/Article.php(2025): WikiPage->getActionOverrides()
#6 /var/lib/mediawiki/w/includes/actions/ActionFactory.php(258): Article->getActionOverrides()
#7 /var/lib/mediawiki/w/includes/actions/ActionFactory.php(404): MediaWiki\Actions\ActionFactory->getAction()
#8 /var/lib/mediawiki/w/includes/context/RequestContext.php(306): MediaWiki\Actions\ActionFactory->getActionName()
#9 /var/lib/mediawiki/w/extensions/Gadgets/includes/GadgetLoadConditions.php(51): RequestContext->getActionName()
#10 /var/lib/mediawiki/w/extensions/Gadgets/includes/Hooks.php(285): MediaWiki\Extension\Gadgets\GadgetLoadConditions->__construct()
#11 /var/lib/mediawiki/w/includes/HookContainer/HookContainer.php(161): MediaWiki\Extension\Gadgets\Hooks->onBeforePageDisplay()
#12 /var/lib/mediawiki/w/includes/HookContainer/HookRunner.php(938): MediaWiki\HookContainer\HookContainer->run()
#13 /var/lib/mediawiki/w/includes/Output/OutputPage.php(2942): MediaWiki\HookContainer\HookRunner->onBeforePageDisplay()
#14 /var/lib/mediawiki/w/includes/exception/MWExceptionRenderer.php(188): MediaWiki\Output\OutputPage->output()
#15 /var/lib/mediawiki/w/includes/exception/MWExceptionRenderer.php(105): MWExceptionRenderer::reportHTML()
#16 /var/lib/mediawiki/w/includes/exception/MWExceptionHandler.php(134): MWExceptionRenderer::output()
#17 /var/lib/mediawiki/w/includes/exception/MWExceptionHandler.php(251): MWExceptionHandler::report()
#18 /var/lib/mediawiki/w/includes/MediaWiki.php(632): MWExceptionHandler::handleException()
#19 /var/lib/mediawiki/w/index.php(50): MediaWiki->run()
#20 /var/lib/mediawiki/w/index.php(46): wfIndexMain()
#21 {main}