Merge -r 585408:585409 from trunk to 0.15 branch. Fixes HADOOP-1973.

git-svn-id: https://svn.apache.org/repos/asf/lucene/hadoop/branches/branch-0.15@585410 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -303,6 +303,11 @@ Branch 0.15 (unreleased changes)
     than the InterruptedException. This behavior is there for the other long
     running threads in the JobTracker. (Arun C Murthy via ddas)
 
+    HADOOP-1973. The FileSystem object would be accessed on the JobTracker
+    through a RPC in the InterTrackerProtocol. The check for the object being
+    null was missing and hence NPE would be thrown sometimes. This issue fixes
+    that problem.  (Amareshwari Sri Ramadasu via ddas) 
+
   IMPROVEMENTS
 
     HADOOP-1908. Restructure data node code so that block sending and 

src/java/org/apache/hadoop/mapred/JobTracker.java

@@ -1471,6 +1471,9 @@ public class JobTracker implements MRConstants, InterTrackerProtocol, JobSubmiss
    * Grab the local fs name
    */
   public synchronized String getFilesystemName() throws IOException {
+    if (fs == null) {
+      throw new IllegalStateException("FileSystem object not available yet");
+    }
     return fs.getName();
   }