Fix a logging NPE problem

bug:6864064
Change-Id: I3237e55cb164462b9616515b0de009bf687f1dca
diff --git a/telephony/java/com/android/internal/telephony/cdma/CdmaServiceStateTracker.java b/telephony/java/com/android/internal/telephony/cdma/CdmaServiceStateTracker.java
index 25cd112..564ce3b 100755
--- a/telephony/java/com/android/internal/telephony/cdma/CdmaServiceStateTracker.java
+++ b/telephony/java/com/android/internal/telephony/cdma/CdmaServiceStateTracker.java
@@ -1378,7 +1378,8 @@
                 mZoneTime    = c.getTimeInMillis();
             }
             if (DBG) {
-                log("NITZ: tzOffset=" + tzOffset + " dst=" + dst + " zone=" + zone.getID() +
+                log("NITZ: tzOffset=" + tzOffset + " dst=" + dst + " zone=" +
+                        (zone!=null ? zone.getID() : "NULL") +
                         " iso=" + iso + " mGotCountryCode=" + mGotCountryCode +
                         " mNeedFixZone=" + mNeedFixZone);
             }