When accessing a planning configuration, there is a PHP notice raised:

Notice: Only variables should be passed by reference in /usr/share/tuleap/plugins/cardwall/include/OnTop/Config/View/ColumnDefinition.class.php on line 261
Call Stack
# Time Memory Function Location
1 0.0002 404552 {main}( ) .../index.php:0
2 0.0108 2413744 Tuleap\Request\FrontRouter->route( ) .../index.php:46
3 0.0129 2606472 Tuleap\Request\FrontRouter->routeHandler( ) .../FrontRouter.php:101
4 0.0298 3209808 Tuleap\AgileDashboard\AgileDashboardLegacyController->process( ) .../FrontRouter.php:232
5 0.0400 3770912 AgileDashboardRouter->route( ) .../AgileDashboardLegacyController.php:59
6 0.0408 3876056 AgileDashboardRouter->renderAction( ) .../AgileDashboardRouter.class.php:206
7 0.0408 3876056 AgileDashboardRouter->executeAction( ) .../AgileDashboardRouter.class.php:450
8 0.0408 3876056 Planning_Controller->edit( ) .../AgileDashboardRouter.class.php:470
9 0.0439 4006264 Planning_Controller->getFormPresenter( ) .../PlanningController.class.php:618
10 0.0544 4080864 Planning_Controller->getCardwallConfiguration( ) .../PlanningController.class.php:628
11 0.0544 4081264 EventManager->processEvent( ) .../PlanningController.class.php:690
12 0.0544 4081264 EventManager->processEventOnListener( ) .../EventManager.class.php:107
13 0.0545 4081264 Tuleap\Plugin\PluginLoader->Tuleap\Plugin\{closure:/usr/share/tuleap/src/common/plugin/PluginLoader.php:61-64}( ) .../EventManager.class.php:119
14 0.0545 4081576 EventManager->eventManagerDispatch( ) .../PluginLoader.php:63
15 0.0545 4081576 cardwallPlugin->agiledashboard_event_planning_config( ) .../EventManager.class.php:130
16 0.0556 4166224 Cardwall_OnTop_Config_View_Admin->displayAdminOnTop( ) .../cardwallPlugin.class.php:555
17 0.0556 4166224 Cardwall_OnTop_Config_View_Admin->generateAdminForm( ) .../Admin.class.php:28
18 0.0569 4166120 Cardwall_OnTop_Config_View_ColumnDefinition->fetchColumnDefinition( ) .../Admin.class.php:46
19 0.0578 4170872 Cardwall_OnTop_Config_View_ColumnDefinition->fetchMappings( ) .../ColumnDefinition.class.php:47
20 0.0609 4215912 Cardwall_OnTop_Config_View_ColumnDefinition->fetchAdditionalColumnHeader( ) .../ColumnDefinition.class.php:73
21 0.0609 4215912 Cardwall_OnTop_Config_View_ColumnDefinition->getPlaceholderSuggestion( ) .../ColumnDefinition.class.php:249