title: Hbase countRow Nullpointer exception at validateArgAndGetPB
body: <p>Hello I'm working with Hbase.
  I want to count Rows of my table, so I used AggregationClient.rowCount()</p>
  
  <pre><code>        Configuration conf = HBaseConfiguration.create();
      AggregationClient aggregationClient = new AggregationClient(conf);
      HTable htable=new HTable(conf,Bytes.toBytes("comment"));
      Scan scan =  new  Scan();
      scan.addFamily(Bytes.toBytes("user"));
      try{
          long  rowCount = aggregationClient.rowCount( htable ,  null , scan);
          System.out.println("Row Count : "+rowCount);
  
      }catch(Throwable e) {
          e.printStackTrace();
      }
  </code></pre>
  
  <p>However I met null point exception </p>
  
  <blockquote>
    <p>java.lang.NullPointerException
        at org.apache.hadoop.hbase.client.coprocessor.AggregationClient.validateArgAndGetPB(AggregationClient.java:804)
        at org.apache.hadoop.hbase.client.coprocessor.AggregationClient.rowCount(AggregationClient.java:306)
        at com.naver.hbase.Main.countRows(Main.java:131)
        at com.naver.hbase.Main.main(Main.java:58)</p>
  </blockquote>
  
  <p>How can I solve it?</p>