Added nullptr check to pullFaceSettingsLocked

Fixes: 175852187
Test: It builds.
Change-Id: Id1eb98f071a96178de42285bb21ef7009517f748
(cherry picked from commit dab89bdde3893e53eb9a7df7f54fff3b2f4c5029)
diff --git a/services/core/java/com/android/server/stats/pull/StatsPullAtomService.java b/services/core/java/com/android/server/stats/pull/StatsPullAtomService.java
index 486de39..68ff022 100644
--- a/services/core/java/com/android/server/stats/pull/StatsPullAtomService.java
+++ b/services/core/java/com/android/server/stats/pull/StatsPullAtomService.java
@@ -3362,7 +3362,11 @@
     int pullFaceSettingsLocked(int atomTag, List<StatsEvent> pulledData) {
         final long callingToken = Binder.clearCallingIdentity();
         try {
-            List<UserInfo> users = mContext.getSystemService(UserManager.class).getUsers();
+            UserManager manager = mContext.getSystemService(UserManager.class);
+            if (manager == null) {
+                return StatsManager.PULL_SKIP;
+            }
+            List<UserInfo> users = manager.getUsers();
             int numUsers = users.size();
             FaceManager faceManager = mContext.getSystemService(FaceManager.class);