Seems to only happen on svwiki for some reason. Apparently $event->getTitle() is null.
2015-09-21 11:33:14 mw1117 svwiki exception ERROR: [ce7c5d6f] /w/api.php?action=query&format=json&meta=notifications¬sections=alert%7Cmessage¬groupbysection=1¬messageunreadfirst=1¬format=flyout¬limit=25¬prop=index%7Clist%7Ccount&uselang=sv&_=1442835190661 EchoCatchableFatalErrorException from line 515 of /srv/mediawiki/php-1.26wmf23/extensions/Flow/includes/UrlGenerator.php: Catchable fatal error: Argument 1 passed to Flow\UrlGenerator::boardLink() must be an instance of Title, null given {"exception_id":"ce7c5d6f"} [Exception EchoCatchableFatalErrorException] (/srv/mediawiki/php-1.26wmf23/extensions/Flow/includes/UrlGenerator.php:515) Catchable fatal error: Argument 1 passed to Flow\UrlGenerator::boardLink() must be an instance of Title, null given #0 /srv/mediawiki/php-1.26wmf23/extensions/Flow/includes/UrlGenerator.php(515): EchoNotificationController::formatterErrorHandler(integer, string, string, integer) #1 /srv/mediawiki/php-1.26wmf23/extensions/Flow/includes/Notifications/Formatter.php(60): Flow\UrlGenerator->boardLink(NULL, string) #2 /srv/mediawiki/php-1.26wmf23/extensions/Flow/includes/Notifications/Formatter.php(244): Flow\NotificationFormatter->processParam(EchoEvent, string, Message, User) #3 /srv/mediawiki/php-1.26wmf23/extensions/Echo/includes/formatters/BasicFormatter.php(647): Flow\NewTopicFormatter->processParam(EchoEvent, string, Message, User) #4 /srv/mediawiki/php-1.26wmf23/extensions/Echo/includes/formatters/BasicFormatter.php(352): EchoBasicFormatter->processParams(array, EchoEvent, Message, User) #5 /srv/mediawiki/php-1.26wmf23/extensions/Echo/includes/formatters/BasicFormatter.php(236): EchoBasicFormatter->formatFragment(array, EchoEvent, User) #6 /srv/mediawiki/php-1.26wmf23/extensions/Echo/includes/formatters/BasicFormatter.php(198): EchoBasicFormatter->formatNotificationTitle(EchoEvent, User) #7 /srv/mediawiki/php-1.26wmf23/extensions/Echo/includes/controller/NotificationController.php(376): EchoBasicFormatter->format(EchoEvent, User, string) #8 /srv/mediawiki/php-1.26wmf23/extensions/Echo/includes/DataOutputFormatter.php(105): EchoNotificationController::formatNotification(EchoEvent, User, string) #9 /srv/mediawiki/php-1.26wmf23/extensions/Echo/includes/api/ApiEchoNotifications.php(155): EchoDataOutputFormatter::formatOutput(EchoNotification, string, User) #10 /srv/mediawiki/php-1.26wmf23/extensions/Echo/includes/api/ApiEchoNotifications.php(94): ApiEchoNotifications->getPropList(User, array, integer, NULL, string, boolean) #11 /srv/mediawiki/php-1.26wmf23/extensions/Echo/includes/api/ApiEchoNotifications.php(30): ApiEchoNotifications->getSectionPropList(User, string, integer, NULL, string, boolean) #12 /srv/mediawiki/php-1.26wmf23/includes/api/ApiQuery.php(286): ApiEchoNotifications->execute() #13 /srv/mediawiki/php-1.26wmf23/includes/api/ApiMain.php(1270): ApiQuery->execute() #14 /srv/mediawiki/php-1.26wmf23/includes/api/ApiMain.php(466): ApiMain->executeAction() #15 /srv/mediawiki/php-1.26wmf23/includes/api/ApiMain.php(438): ApiMain->executeActionWithErrorHandling() #16 /srv/mediawiki/php-1.26wmf23/api.php(88): ApiMain->execute() #17 /srv/mediawiki/w/api.php(3): include(string) #18 {main}