Merge "Avoid the scenario where Contexts list filled with null value in ShowAnrDialogs()" am: 99e5c70ff0

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1793211

Change-Id: I27e6901083d1f16c2b2bcccb77627c81592d4ceb

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

@@ -908,7 +908,7 @@ public class WindowProcessController extends ConfigurationContainer<Configuratio
                 final int displayId = r.getDisplayId();
                 final Context c = root.getDisplayUiContext(displayId);
 
-                if (r.mVisibleRequested && !displayContexts.contains(c)) {
+                if (c != null && r.mVisibleRequested && !displayContexts.contains(c)) {
                     displayContexts.add(c);
                 }
             }