merge MAPREDUCE-3630 from trunk

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1235642 13f79535-47bb-0310-9956-ffa450edef68

hadoop-mapreduce-project/CHANGES.txt

@@ -510,6 +510,9 @@ Release 0.23.1 - Unreleased
     MAPREDUCE-3717. JobClient test jar has missing files to run all the test programs.
     (mahadev)
 
+    MAPREDUCE-3630. Fixes a NullPointer exception while running TeraGen - if a
+    map is asked to generate 0 records. (Mahadev Konar via sseth)
+
 Release 0.23.0 - 2011-11-01 
 
   INCOMPATIBLE CHANGES

hadoop-mapreduce-project/hadoop-mapreduce-examples/src/main/java/org/apache/hadoop/examples/terasort/TeraGen.java

@@ -238,7 +238,9 @@ public class TeraGen extends Configured implements Tool {
 
     @Override
     public void cleanup(Context context) {
-      checksumCounter.increment(total.getLow8());
+      if (checksumCounter != null) {
+        checksumCounter.increment(total.getLow8());
+      }
     }
   }
 
@@ -307,5 +309,4 @@ public class TeraGen extends Configured implements Tool {
     int res = ToolRunner.run(new Configuration(), new TeraGen(), args);
     System.exit(res);
   }
-
 }