Null check.

Change-Id: I16dfe2cf265b4254aa69bc6165a8f72fc3954d7a
Fixes: 28531037

src/com/android/settings/datausage/AppDataUsage.java

@@ -302,7 +302,10 @@ public class AppDataUsage extends DataUsageBase implements Preference.OnPreferen
     }
 
     private boolean getUnrestrictData() {
-        return mDataSaverBackend.isWhitelisted(mAppItem.key);
+        if (mDataSaverBackend != null) {
+            return mDataSaverBackend.isWhitelisted(mAppItem.key);
+        }
+        return false;
     }
 
     @Override