Check the nullity of display when remove starting window

Bug: 278268592
Test: ABTD run.
Change-Id: I7313957e6f266d1b55173f109286e75037495109

services/core/java/com/android/server/wm/TaskOrganizerController.java

@@ -681,6 +681,7 @@ class TaskOrganizerController extends ITaskOrganizerController.Stub {
         final StartingWindowRemovalInfo removalInfo = new StartingWindowRemovalInfo();
         removalInfo.taskId = task.mTaskId;
         removalInfo.playRevealAnimation = prepareAnimation
+                && task.getDisplayContent() != null
                 && task.getDisplayInfo().state == Display.STATE_ON;
         final boolean playShiftUpAnimation = !task.inMultiWindowMode();
         final ActivityRecord topActivity = task.topActivityContainsStartingWindow();