Internal error

From cnl wiki

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

Backtrace:

#0 /ext/opt/tw/htdocs/html/tw.rpi.edu/proj/cnl.wiki/includes/OutputPage.php(445): wfRunHooks('OutputPageParse...', Array)
#1 /ext/opt/tw/htdocs/html/tw.rpi.edu/proj/cnl.wiki/includes/OutputPage.php(453): OutputPage->addParserOutputNoText(Object(ParserOutput))
#2 /ext/opt/tw/htdocs/html/tw.rpi.edu/proj/cnl.wiki/includes/OutputPage.php(543): OutputPage->addParserOutput(Object(ParserOutput))
#3 /ext/opt/tw/htdocs/html/tw.rpi.edu/proj/cnl.wiki/includes/Article.php(794): OutputPage->tryParserCache(Object(Article), Object(User))
#4 /ext/opt/tw/htdocs/html/tw.rpi.edu/proj/cnl.wiki/includes/Wiki.php(437): Article->view()
#5 /ext/opt/tw/htdocs/html/tw.rpi.edu/proj/cnl.wiki/includes/Wiki.php(59): MediaWiki->performAction(Object(OutputPage), Object(Article), Object(Title), Object(User), Object(WebRequest))
#6 /ext/opt/tw/htdocs/html/tw.rpi.edu/proj/cnl.wiki/index.php(93): MediaWiki->initialize(Object(Title), Object(Article), Object(OutputPage), Object(User), Object(WebRequest))
#7 {main}