MediaWiki internal error.

Original exception: [ZgZ3wqFJofnouBk7mvp8QAAAAAI] /wiki/index.php?title=Clans(CoffeeMUD)&oldid=6528 Error from line 3168 of /usr/share/mediawiki/includes/parser/Parser.php: Call to a member function matchStartAndRemove() on null
Backtrace:
#0 /usr/share/mediawiki/includes/parser/Preprocessor_DOM.php(1285): Parser->braceSubstitution()
#1 /usr/share/mediawiki/includes/parser/Parser.php(3049): PPFrame_DOM->expand()
#2 /usr/share/mediawiki/includes/parser/Parser.php(749): Parser->replaceVariables()
#3 /usr/share/mediawiki/includes/parser/Parser.php(4829): Parser->preprocess()
#4 /usr/share/mediawiki/includes/cache/MessageCache.php(1192): Parser->transformMsg()
#5 /usr/share/mediawiki/includes/Message.php(1291): MessageCache->transform()
#6 /usr/share/mediawiki/includes/Message.php(895): Message->transformText()
#7 /usr/share/mediawiki/includes/Message.php(955): Message->toString()
#8 /usr/share/mediawiki/includes/exception/MWExceptionRenderer.php(203): Message->text()
#9 /usr/share/mediawiki/includes/exception/MWExceptionRenderer.php(142): MWExceptionRenderer::msg()
#10 /usr/share/mediawiki/includes/exception/MWExceptionRenderer.php(53): MWExceptionRenderer::reportHTML()
#11 /usr/share/mediawiki/includes/exception/MWExceptionHandler.php(98): MWExceptionRenderer::output()
#12 /usr/share/mediawiki/includes/exception/MWExceptionHandler.php(172): MWExceptionHandler::report()
#13 /usr/share/mediawiki/includes/MediaWiki.php(542): MWExceptionHandler::handleException()
#14 /usr/share/mediawiki/index.php(42): MediaWiki->run()
#15 {main}

Exception caught inside exception handler: [ZgZ3wqFJofnouBk7mvp8QAAAAAI] /wiki/index.php?title=Clans(CoffeeMUD)&oldid=6528 Wikimedia\Rdbms\DBConnectionError from line 1213 of /usr/share/mediawiki/includes/libs/rdbms/loadbalancer/LoadBalancer.php: Cannot access the database: Unknown error (localhost)
Backtrace:
#0 /usr/share/mediawiki/includes/libs/rdbms/loadbalancer/LoadBalancer.php(758): Wikimedia\Rdbms\LoadBalancer->reportConnectionError()
#1 /usr/share/mediawiki/includes/GlobalFunctions.php(2649): Wikimedia\Rdbms\LoadBalancer->getConnection()
#2 /usr/share/mediawiki/includes/cache/LinkBatch.php(199): wfGetDB()
#3 /usr/share/mediawiki/includes/cache/LinkBatch.php(141): LinkBatch->doQuery()
#4 /usr/share/mediawiki/includes/cache/LinkBatch.php(130): LinkBatch->executeInto()
#5 /usr/share/mediawiki/includes/skins/Skin.php(300): LinkBatch->execute()
#6 /usr/share/mediawiki/includes/skins/Skin.php(163): Skin->preloadExistence()
#7 /usr/share/mediawiki/skins/Vector/includes/SkinVector.php(67): Skin->initPage()
#8 /usr/share/mediawiki/includes/skins/SkinTemplate.php(227): SkinVector->initPage()
#9 /usr/share/mediawiki/includes/OutputPage.php(2723): SkinTemplate->outputPage()
#10 /usr/share/mediawiki/includes/exception/MWExceptionRenderer.php(134): OutputPage->output()
#11 /usr/share/mediawiki/includes/exception/MWExceptionRenderer.php(53): MWExceptionRenderer::reportHTML()
#12 /usr/share/mediawiki/includes/exception/MWExceptionHandler.php(98): MWExceptionRenderer::output()
#13 /usr/share/mediawiki/includes/exception/MWExceptionHandler.php(172): MWExceptionHandler::report()
#14 /usr/share/mediawiki/includes/exception/MWExceptionHandler.php(144): MWExceptionHandler::handleException()
#15 [internal function]: MWExceptionHandler::handleUncaughtException()
#16 {main}