Fixed SystemServiceRegistry to return a null AppPredictionManager when the service is not defined.

Test: manual verification
Test: atest CtsAssistTestCases

Fixes: 139416391

Change-Id: Ieb2ae3f39bd42dc077ed3db1c6acdf429a39d519

core/java/android/app/SystemServiceRegistry.java

@@ -1166,7 +1166,8 @@ public final class SystemServiceRegistry {
             @Override
             public AppPredictionManager createService(ContextImpl ctx)
                     throws ServiceNotFoundException {
-                return new AppPredictionManager(ctx);
+                IBinder b = ServiceManager.getService(Context.APP_PREDICTION_SERVICE);
+                return b == null ? null : new AppPredictionManager(ctx);
             }
         });
 

core/java/android/content/Context.java

@@ -4109,6 +4109,9 @@ public abstract class Context {
     /**
      * Official published name of the app prediction service.
      *
+     * <p><b>NOTE: </b> this service is optional; callers of
+     * {@code Context.getSystemServiceName(APP_PREDICTION_SERVICE)} should check for {@code null}.
+     *
      * @hide
      * @see #getSystemService(String)
      */