Throw NPE if s is null

Bug: 5926510
Change-Id: I3d0a38d31695a8b103b3d153d90d83474f56990e

Author: alonalbert

core/java/android/text/format/Time.java

@@ -481,6 +481,9 @@ public boolean parse(String s) {
      * @throws android.util.TimeFormatException if s cannot be parsed.
      */
      public boolean parse3339(String s) {
+         if (s == null) {
+             throw new NullPointerException("time string is null");
+         }
          if (nativeParse3339(s)) {
              timezone = TIMEZONE_UTC;
              return true;