this is somewhat frequent in the logs
/w/index.php?title=%E7%89%B9%E5%88%A5:MathShowImage&hash=773282d0f15f7cd9b50ac4b8268c896a&mode=mathml BadMethodCallException from line 29 of /srv/mediawiki/php-1.26wmf17/extensions/Graph/Graph.body.php: Call to a member function getIsPreview() on a non-object (NULL) { "exception":" [Exception BadMethodCallException] (/srv/mediawiki/php-1.26wmf17/extensions/Graph/Graph.body.php:29) Call to a member function getIsPreview() on a non-object (NULL) [stacktrace] #0 /srv/mediawiki/php-1.26wmf17/includes/Hooks.php(204): Graph\\Singleton::onParserAfterParse(Parser) #1 /srv/mediawiki/php-1.26wmf17/extensions/Math/MathTexvc.php(397): Hooks::run(string, array) #2 /srv/mediawiki/php-1.26wmf17/extensions/Math/SpecialMathShowImage.php(96): MathTexvc->getPng() #3 /srv/mediawiki/php-1.26wmf17/includes/specialpage/SpecialPage.php(384): SpecialMathShowImage->execute(NULL) #4 /srv/mediawiki/php-1.26wmf17/includes/specialpage/SpecialPageFactory.php(553): SpecialPage->run(NULL) #5 /srv/mediawiki/php-1.26wmf17/includes/MediaWiki.php(249): SpecialPageFactory::executePath(Title, RequestContext) #6 /srv/mediawiki/php-1.26wmf17/includes/MediaWiki.php(677): MediaWiki->performRequest() #7 /srv/mediawiki/php-1.26wmf17/includes/MediaWiki.php(474): MediaWiki->main() #8 /srv/mediawiki/php-1.26wmf17/index.php(41): MediaWiki->run() #9 /srv/mediawiki/w/index.php(3): include(string) #10 {main} "}