public WriteBuffers.ByteSegmentRef next() {
      if (!hasRows) {
        return null;
      }

      return internalRead();
    }
Set internal values for reading the values after finding a key.

@param hashMap
         The hash map we found the key in.
@param firstOffset
         The absolute offset of the first record in the write buffers.
@param hasList
         Whether there are multiple values (true) or just a single value (false).
@param offsetAfterListRecordKeyLen
         The offset of just after the key length in the list record.  Or, 0 when single row.
ql/src/java/org/apache/hadoop/hive/ql/exec/persistence/BytesBytesMultiHashMap.java