Internal error

Detected bug in an extension! Hook ConfirmEditHooks::confirmEditMerged failed to return a value; should return true to continue hook processing or false to abort.

Backtrace:

#0 /usr/share/mediawiki/includes/EditPage.php(956): wfRunHooks('EditFilterMerge...', Array)
#1 /usr/share/mediawiki/includes/EditPage.php(2483): EditPage->internalAttemptSave(false, false)
#2 /usr/share/mediawiki/includes/EditPage.php(449): EditPage->attemptSave()
#3 /usr/share/mediawiki/includes/EditPage.php(340): EditPage->edit()
#4 /usr/share/mediawiki/includes/Wiki.php(510): EditPage->submit()
#5 /usr/share/mediawiki/includes/Wiki.php(63): MediaWiki->performAction(Object(OutputPage), Object(Article), Object(Title), Object(User), Object(WebRequest))
#6 /usr/share/mediawiki/index.php(116): MediaWiki->initialize(Object(Title), Object(Article), Object(OutputPage), Object(User), Object(WebRequest))
#7 {main}