HDFS-7383. Merged to branch-2.6 also.

(cherry picked from commit f62ec31739cc15097107655c6c8265b5d3625817)

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -1273,6 +1273,9 @@ Release 2.6.0 - UNRELEASED
     HDFS-7382. DataNode in secure mode may throw NullPointerException if client
     connects before DataNode registers itself with NameNode. (cnauroth)
 
+    HDFS-7383. DataNode.requestShortCircuitFdsForRead may throw 
+    NullPointerException. (szetszwo via suresh)
+
 Release 2.5.2 - UNRELEASED
 
   INCOMPATIBLE CHANGES