title: Nullpointer exception in HBase MapReduce
body: <p>I have a mapreduce app that takes an HBase source data and mapreduces it to another HBase table, all written in Java.When I run it using </p>
  
  <pre><code>hadoop jar myhbase.jar 
  </code></pre>
  
  <p>It terminated with a <code>NullpointerException</code>
  as below:</p>
  
  <pre><code>
  14/01/31 11:07:02 INFO zookeeper.ClientCnxn: Socket connection established to 127.0.0.1/127.0.0.1:2181, initiating session
  14/01/31 11:07:02 INFO zookeeper.ClientCnxn: Session establishment complete on server 127.0.0.1/127.0.0.1:2181, sessionid = 0x143e677d6e30007, negotiated timeout = 180000
  14/01/31 11:07:03 INFO mapreduce.TableOutputFormat: Created table instance for hourinfo
  14/01/31 11:07:03 INFO mapred.JobClient: Cleaning up the staging area hdfs://192.168.1.149:9000/hadoop_tmp/mapred/staging/root/.staging/job_201401310933_0002
  Exception in thread "main" java.lang.NullPointerException
          at org.apache.hadoop.net.DNS.reverseDns(DNS.java:72)
          at org.apache.hadoop.hbase.mapreduce.TableInputFormatBase.reverseDNS(TableInputFormatBase.java:219)
          at org.apache.hadoop.hbase.mapreduce.TableInputFormatBase.getSplits(TableInputFormatBase.java:184)
          at org.apache.hadoop.mapred.JobClient.writeNewSplits(JobClient.java:962)
          at org.apache.hadoop.mapred.JobClient.writeSplits(JobClient.java:979)
          at org.apache.hadoop.mapred.JobClient.access$600(JobClient.java:174)
          at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:897)
          at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:850)
          at java.security.AccessController.doPrivileged(Native Method)
          at javax.security.auth.Subject.doAs(Subject.java:396)
          at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1121)
          at org.apache.hadoop.mapred.JobClient.submitJobInternal(JobClient.java:850)
          at org.apache.hadoop.mapreduce.Job.submit(Job.java:500)
          at org.apache.hadoop.mapreduce.Job.waitForCompletion(Job.java:530)
          at mapreduce.hi.api.hbase.HBaseJobRunner.main(HBaseJobRunner.java:37)
          at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
          at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
          at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
          at java.lang.reflect.Method.invoke(Method.java:597)
          at org.apache.hadoop.util.RunJar.main(RunJar.java:156)
  
  </code></pre>
  
  <p>I am using <code>hbase-0.94.5</code> and <code>hadoop-1.0.4</code>. I am really stuck on this error.Please help..</p>