To reproduce the issue:
1. Create a tracker without a status semantic defined
2. Create a kanban a using this tracker
3. Update an artifact in this tracker

The use case of having a kanban based on a tracker without a status semantic is weird, it should probably not be possible.

Trace:
Fatal error: Call to a member function getId() on null in /usr/share/tuleap/plugins/agiledashboard/include/AgileDashboard/Kanban/RealTime/KanbanArtifactMessageBuilder.php on line 75
Call Stack
# Time Memory Function Location
1 0.0000 257104 {main}( ) ../index.php:0
2 0.0368 7211648 TrackerManager->process( ) ../index.php:35
3 0.0368 7212240 TrackerManager->processSubElement( ) ../TrackerManager.class.php:161
4 0.0432 7704792 Tracker_Artifact->process( ) ../TrackerManager.class.php:105
5 0.0437 7754160 Tracker_Action_UpdateArtifact->process( ) ../Tracker_Artifact.class.php:670
6 0.0463 8441456 Tracker_Artifact->createNewChangeset( ) ../UpdateArtifact.class.php:68
7 0.0474 8539392 Tracker_Artifact_Changeset_NewChangesetCreatorBase->create( ) ../Tracker_Artifact.class.php:1059
8 0.1766 10023096 EventManager->processEvent( ) ../NewChangesetCreatorBase.class.php:159
9 0.1766 10023096 EventManager->processEventOnListener( ) ../EventManager.class.php:94
10 0.1766 10023096 PluginProxy->processEvent( ) ../EventManager.class.php:106
11 0.1766 10023176 AgileDashboardPlugin->tracker_event_artifact_post_update( ) ../PluginProxy.php:64
12 0.1782 10101832 Tuleap\AgileDashboard\RealTime\RealTimeArtifactMessageController->sendMessageForKanban( ) ../agiledashboardPlugin.class.php:1285
13 0.1824 10179888 Tuleap\AgileDashboard\Kanban\RealTime\KanbanArtifactMessageSender->sendMessageArtifactMoved( ) ../RealTimeArtifactMessageController.php:77
14 0.1824 10180304 Tuleap\AgileDashboard\Kanban\RealTime\KanbanArtifactMessageBuilder->buildArtifactMoved( ) ../KanbanArtifactMessageSender.php:84