MediaWiki internal error.

Original exception: [7466b708f423d5dbe98ba6cc] /wiki/index.php?title=Form:Material_Thinking&oldid=7341 Wikimedia\Assert\PostconditionException: Postcondition failed: makeTitleSafe() should always return a Title for the text returned by getRootText().
Backtrace:
from /var/www/html/wiki/vendor/wikimedia/assert/src/Assert.php(202)
#0 /var/www/html/wiki/includes/Title.php(2025): Wikimedia\Assert\Assert::postcondition()
#1 /var/www/html/wiki/includes/skins/Skin.php(518): Title->getRootTitle()
#2 /var/www/html/wiki/includes/OutputPage.php(3147): Skin->getPageClasses()
#3 /var/www/html/wiki/includes/skins/SkinTemplate.php(437): OutputPage->headElement()
#4 /var/www/html/wiki/includes/skins/SkinTemplate.php(127): SkinTemplate->prepareQuickTemplate()
#5 /var/www/html/wiki/includes/skins/SkinTemplate.php(144): SkinTemplate->generateHTML()
#6 /var/www/html/wiki/includes/OutputPage.php(2644): SkinTemplate->outputPage()
#7 /var/www/html/wiki/includes/MediaWiki.php(944): OutputPage->output()
#8 /var/www/html/wiki/includes/MediaWiki.php(957): MediaWiki::{closure}()
#9 /var/www/html/wiki/includes/MediaWiki.php(564): MediaWiki->main()
#10 /var/www/html/wiki/index.php(53): MediaWiki->run()
#11 /var/www/html/wiki/index.php(46): wfIndexMain()
#12 {main}

Exception caught inside exception handler: [7466b708f423d5dbe98ba6cc] /wiki/index.php?title=Form:Material_Thinking&oldid=7341 Wikimedia\Assert\PostconditionException: Postcondition failed: makeTitleSafe() should always return a Title for the text returned by getRootText().
Backtrace:
from /var/www/html/wiki/vendor/wikimedia/assert/src/Assert.php(202)
#0 /var/www/html/wiki/includes/Title.php(2025): Wikimedia\Assert\Assert::postcondition()
#1 /var/www/html/wiki/includes/skins/Skin.php(518): Title->getRootTitle()
#2 /var/www/html/wiki/includes/OutputPage.php(3147): Skin->getPageClasses()
#3 /var/www/html/wiki/includes/skins/SkinTemplate.php(437): OutputPage->headElement()
#4 /var/www/html/wiki/includes/skins/SkinTemplate.php(127): SkinTemplate->prepareQuickTemplate()
#5 /var/www/html/wiki/includes/skins/SkinTemplate.php(144): SkinTemplate->generateHTML()
#6 /var/www/html/wiki/includes/OutputPage.php(2644): SkinTemplate->outputPage()
#7 /var/www/html/wiki/includes/exception/MWExceptionRenderer.php(158): OutputPage->output()
#8 /var/www/html/wiki/includes/exception/MWExceptionRenderer.php(77): MWExceptionRenderer::reportHTML()
#9 /var/www/html/wiki/includes/exception/MWExceptionHandler.php(107): MWExceptionRenderer::output()
#10 /var/www/html/wiki/includes/exception/MWExceptionHandler.php(202): MWExceptionHandler::report()
#11 /var/www/html/wiki/includes/MediaWiki.php(583): MWExceptionHandler::handleException()
#12 /var/www/html/wiki/index.php(53): MediaWiki->run()
#13 /var/www/html/wiki/index.php(46): wfIndexMain()
#14 {main}