MediaWiki internal error.

Original exception: [0261f765d9ab97f1496e505e] /index.php?title=Formulier:Meeting&oldid=523 Wikimedia\Assert\PostconditionException from line 140 of /srv/webserver/lugwiki073/vendor/wikimedia/assert/src/Assert.php: Postcondition failed: makeTitleSafe() should always return a Title for the text returned by getRootText().
Backtrace:
#0 /srv/webserver/lugwiki073/includes/Title.php(1893): Wikimedia\Assert\Assert::postcondition(boolean, string)
#1 /srv/webserver/lugwiki073/includes/skins/Skin.php(472): Title->getRootTitle()
#2 /srv/webserver/lugwiki073/skins/Vector/includes/SkinVector.php(47): Skin->getPageClasses(Title)
#3 /srv/webserver/lugwiki073/includes/OutputPage.php(3080): SkinVector->getPageClasses(Title)
#4 /srv/webserver/lugwiki073/includes/skins/SkinTemplate.php(459): OutputPage->headElement(SkinVector)
#5 /srv/webserver/lugwiki073/includes/skins/SkinTemplate.php(215): SkinTemplate->prepareQuickTemplate()
#6 /srv/webserver/lugwiki073/includes/OutputPage.php(2574): SkinTemplate->outputPage()
#7 /srv/webserver/lugwiki073/includes/MediaWiki.php(907): OutputPage->output(boolean)
#8 /srv/webserver/lugwiki073/includes/MediaWiki.php(919): MediaWiki->{closure}()
#9 /srv/webserver/lugwiki073/includes/MediaWiki.php(527): MediaWiki->main()
#10 /srv/webserver/lugwiki073/index.php(44): MediaWiki->run()
#11 {main}

Exception caught inside exception handler: [0261f765d9ab97f1496e505e] /index.php?title=Formulier:Meeting&oldid=523 Wikimedia\Assert\PostconditionException from line 140 of /srv/webserver/lugwiki073/vendor/wikimedia/assert/src/Assert.php: Postcondition failed: makeTitleSafe() should always return a Title for the text returned by getRootText().
Backtrace:
#0 /srv/webserver/lugwiki073/includes/Title.php(1893): Wikimedia\Assert\Assert::postcondition(boolean, string)
#1 /srv/webserver/lugwiki073/includes/skins/Skin.php(472): Title->getRootTitle()
#2 /srv/webserver/lugwiki073/skins/Vector/includes/SkinVector.php(47): Skin->getPageClasses(Title)
#3 /srv/webserver/lugwiki073/includes/OutputPage.php(3080): SkinVector->getPageClasses(Title)
#4 /srv/webserver/lugwiki073/includes/skins/SkinTemplate.php(459): OutputPage->headElement(SkinVector)
#5 /srv/webserver/lugwiki073/includes/skins/SkinTemplate.php(215): SkinTemplate->prepareQuickTemplate()
#6 /srv/webserver/lugwiki073/includes/OutputPage.php(2574): SkinTemplate->outputPage()
#7 /srv/webserver/lugwiki073/includes/exception/MWExceptionRenderer.php(134): OutputPage->output()
#8 /srv/webserver/lugwiki073/includes/exception/MWExceptionRenderer.php(53): MWExceptionRenderer::reportHTML(Wikimedia\Assert\PostconditionException)
#9 /srv/webserver/lugwiki073/includes/exception/MWExceptionHandler.php(121): MWExceptionRenderer::output(Wikimedia\Assert\PostconditionException, integer)
#10 /srv/webserver/lugwiki073/includes/exception/MWExceptionHandler.php(195): MWExceptionHandler::report(Wikimedia\Assert\PostconditionException)
#11 /srv/webserver/lugwiki073/includes/MediaWiki.php(558): MWExceptionHandler::handleException(Wikimedia\Assert\PostconditionException)
#12 /srv/webserver/lugwiki073/index.php(44): MediaWiki->run()
#13 {main}