I'm seeing this (non-critical) error appear when viewing Conpherence threads:
array_key_exists(): The first argument should be either a string or an integer Stack trace: array_key_exists called at [/srv/phabricator/libphutil/src/utils/utils.php:43] idx called at [/srv/phabricator/phabricator/src/applications/conpherence/view/ConpherenceThreadListView.php:25] ConpherenceThreadListView::render called at [/srv/phabricator/phabricator/src/view/AphrontView.php:159] AphrontView::producePhutilSafeHTML called at [/srv/phabricator/libphutil/src/markup/render.php:132] phutil_escape_html called at [/srv/phabricator/libphutil/src/markup/render.php:118] phutil_tag called at [/srv/phabricator/phabricator/src/infrastructure/javelin/markup.php:53] javelin_tag called at [/srv/phabricator/phabricator/src/applications/conpherence/view/ConpherenceLayoutView.php:122] ConpherenceLayoutView::render called at [/srv/phabricator/phabricator/src/view/AphrontView.php:159] AphrontView::producePhutilSafeHTML called at [/srv/phabricator/libphutil/src/markup/render.php:132] phutil_escape_html called at [/srv/phabricator/libphutil/src/markup/render.php:154] phutil_escape_html called at [/srv/phabricator/libphutil/src/markup/render.php:154] phutil_escape_html called at [/srv/phabricator/libphutil/src/markup/render.php:118] phutil_tag called at [/srv/phabricator/phabricator/src/view/layout/AphrontSideNavFilterView.php:327] AphrontSideNavFilterView::renderFlexNav called at [/srv/phabricator/phabricator/src/view/layout/AphrontSideNavFilterView.php:211] AphrontSideNavFilterView::render called at [/srv/phabricator/phabricator/src/view/AphrontView.php:159] AphrontView::producePhutilSafeHTML called at [/srv/phabricator/libphutil/src/markup/render.php:132] phutil_escape_html called at [/srv/phabricator/libphutil/src/markup/render.php:186] phutil_implode_html called at [/srv/phabricator/phabricator/src/view/page/PhabricatorBarePageView.php:58] PhabricatorBarePageView::willRenderPage called at [/srv/phabricator/phabricator/src/view/page/PhabricatorStandardPageView.php:146] PhabricatorStandardPageView::willRenderPage called at [/srv/phabricator/phabricator/src/view/page/AphrontPageView.php:46] AphrontPageView::render called at [/srv/phabricator/phabricator/src/applications/base/controller/PhabricatorController.php:295] PhabricatorController::buildPageResponse called at [/srv/phabricator/phabricator/src/applications/base/controller/PhabricatorController.php:357] PhabricatorController::buildApplicationPage called at [/srv/phabricator/phabricator/src/applications/conpherence/controller/ConpherenceListController.php:111] ConpherenceListController::handleRequest called at [/srv/phabricator/phabricator/src/aphront/configuration/AphrontApplicationConfiguration.php:196] AphrontApplicationConfiguration::processRequest called at [/srv/phabricator/phabricator/src/aphront/configuration/AphrontApplicationConfiguration.php:121] AphrontApplicationConfiguration::runHTTPRequest called at [/srv/phabricator/phabricator/webroot/index.php:19]
You can see it by going to https://code.redpointsoftware.com.au/conpherence/.
This is from upgrading Phabricator about 30 minutes ago to HEAD (plus patches, but nothing that touches Conpherence).