svn merge -c 1483974 FIXES: MAPREDUCE-4927. Historyserver 500 error due to NPE when accessing specific counters page for failed job. Contributed by Ashwin Shankar


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1483976 13f79535-47bb-0310-9956-ffa450edef68