Merge "Avoid the scenario where Contexts list filled with null value in ShowAnrDialogs()" am: 99e5c70ff0 am: 7f2cb4c0a5

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

Change-Id: I00ebb6e21e6ad6f641fe52249b27cd59b77f9da6

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

@@ -940,7 +940,7 @@ 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);
                 }
             }