Internal error

From cchtml.com

[ZgV71olU-G4ooSajjhlu3AAAxQM] /index.php?title=Talk:Fedora_Core_6_Installation_Guide&action=edit&undoafter=4190&undo=4191 Error: Call to a member function getContent() on null

Backtrace:

from /usr/share/mediawiki/includes/EditPage.php(1663)
#0 /usr/share/mediawiki/includes/EditPage.php(1517): EditPage->getUndoContent()
#1 /usr/share/mediawiki/includes/EditPage.php(956): EditPage->getContentObject()
#2 /usr/share/mediawiki/includes/EditPage.php(663): EditPage->displayPermissionsError()
#3 /usr/share/mediawiki/includes/actions/EditAction.php(73): EditPage->edit()
#4 /usr/share/mediawiki/includes/MediaWiki.php(542): EditAction->show()
#5 /usr/share/mediawiki/includes/MediaWiki.php(322): MediaWiki->performAction()
#6 /usr/share/mediawiki/includes/MediaWiki.php(904): MediaWiki->performRequest()
#7 /usr/share/mediawiki/includes/MediaWiki.php(562): MediaWiki->main()
#8 /usr/share/mediawiki/index.php(50): MediaWiki->run()
#9 /usr/share/mediawiki/index.php(46): wfIndexMain()
#10 {main}