HIVE-6537 NullPointerException when loading hashtable for MapJoin directly (Sergey Shelukhin and Navis, reviewed by Gunther Hagleitner)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/branch-0.13@1575353 13f79535-47bb-0310-9956-ffa450edef68