Restored original behavior of getApplicationRestrictions

JavaDoc for getApplicationRestrictions states that null is a valid return
 value, but it turns out some apps do not expect that. This fix restores
the original behavior of returning an empty bundle.

Bug: 20081431
Change-Id: I30a4aa6aba14307eba59ba0015f80f14107269af
diff --git a/services/core/java/com/android/server/pm/UserManagerService.java b/services/core/java/com/android/server/pm/UserManagerService.java
index b8c26a4..a8c5527 100644
--- a/services/core/java/com/android/server/pm/UserManagerService.java
+++ b/services/core/java/com/android/server/pm/UserManagerService.java
@@ -1690,7 +1690,7 @@
         final Bundle restrictions = new Bundle();
         final ArrayList<String> values = new ArrayList<>();
         if (!restrictionsFile.getBaseFile().exists()) {
-            return null;
+            return restrictions;
         }
 
         FileInputStream fis = null;