MediaWiki internal error.

Original exception: [e96a2a732c91693fc7c97ff6] /index.php?title=Wordpress:Fu%C3%9Fnoten_einf%C3%BCgen&diff=prev&oldid=2226 Wikimedia\Assert\PostconditionException from line 140 of /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/vendor/wikimedia/assert/src/Assert.php: Postcondition failed: makeTitleSafe() should always return a Title for the text returned by getRootText().
Backtrace:
#0 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/includes/Title.php(1893): Wikimedia\Assert\Assert::postcondition(boolean, string)
#1 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/includes/skins/Skin.php(472): Title->getRootTitle()
#2 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/skins/Vector/includes/SkinVector.php(47): Skin->getPageClasses(Title)
#3 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/includes/OutputPage.php(3080): SkinVector->getPageClasses(Title)
#4 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/includes/skins/SkinTemplate.php(459): OutputPage->headElement(SkinVector)
#5 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/includes/skins/SkinTemplate.php(215): SkinTemplate->prepareQuickTemplate()
#6 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/includes/OutputPage.php(2574): SkinTemplate->outputPage()
#7 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/includes/MediaWiki.php(907): OutputPage->output(boolean)
#8 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/includes/MediaWiki.php(919): MediaWiki->{closure}()
#9 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/includes/MediaWiki.php(527): MediaWiki->main()
#10 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/index.php(44): MediaWiki->run()
#11 {main}

Exception caught inside exception handler: [e96a2a732c91693fc7c97ff6] /index.php?title=Wordpress:Fu%C3%9Fnoten_einf%C3%BCgen&diff=prev&oldid=2226 Wikimedia\Assert\PostconditionException from line 140 of /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/vendor/wikimedia/assert/src/Assert.php: Postcondition failed: makeTitleSafe() should always return a Title for the text returned by getRootText().
Backtrace:
#0 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/includes/Title.php(1893): Wikimedia\Assert\Assert::postcondition(boolean, string)
#1 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/includes/skins/Skin.php(472): Title->getRootTitle()
#2 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/skins/Vector/includes/SkinVector.php(47): Skin->getPageClasses(Title)
#3 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/includes/OutputPage.php(3080): SkinVector->getPageClasses(Title)
#4 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/includes/skins/SkinTemplate.php(459): OutputPage->headElement(SkinVector)
#5 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/includes/skins/SkinTemplate.php(215): SkinTemplate->prepareQuickTemplate()
#6 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/includes/OutputPage.php(2574): SkinTemplate->outputPage()
#7 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/includes/exception/MWExceptionRenderer.php(134): OutputPage->output()
#8 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/includes/exception/MWExceptionRenderer.php(53): MWExceptionRenderer::reportHTML(Wikimedia\Assert\PostconditionException)
#9 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/includes/exception/MWExceptionHandler.php(121): MWExceptionRenderer::output(Wikimedia\Assert\PostconditionException, integer)
#10 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/includes/exception/MWExceptionHandler.php(195): MWExceptionHandler::report(Wikimedia\Assert\PostconditionException)
#11 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/includes/MediaWiki.php(558): MWExceptionHandler::handleException(Wikimedia\Assert\PostconditionException)
#12 /var/www/vhosts/h287025.server26.campusspeicher.de/wiki.velocityruhr.net/mediawiki-1.34.1/index.php(44): MediaWiki->run()
#13 {main}