Merge "Fix NPE on WindowContainer#isOnTop" into rvc-dev am: e0ac89603b am: 86366e59cb

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/11882882

Change-Id: Ibd8cb61436c32567e87f797f9243905417836e5b

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

@@ -1032,7 +1032,8 @@ class WindowContainer<E extends WindowContainer> extends ConfigurationContainer<
      * @return Whether this child is on top of the window hierarchy.
      */
     boolean isOnTop() {
-        return getParent().getTopChild() == this && getParent().isOnTop();
+        final WindowContainer parent = getParent();
+        return parent != null && parent.getTopChild() == this && parent.isOnTop();
     }
 
     /** Returns the top child container. */