@Override
    public boolean next(Object key, Object value) throws IOException {
      if (processed) {
        return false;
      }
      processed = true;
      if (rbCtx != null) {
        makeNullVrb(value, 1);
      }
      return true;
    }
OneNullRowInputFormat outputs one null row. Used in implementation of
metadata only queries.
ql/src/java/org/apache/hadoop/hive/ql/io/OneNullRowInputFormat.java