code: private static boolean isStatisticsPosition(Page page, int position)
      {
          return page.getBlock(ROW_COUNT_CHANNEL).isNull(position) && page.getBlock(FRAGMENT_CHANNEL).isNull(position);
      }
docs: Both the statistics and the row_count + fragments are transferred over the same communication
  link between the TableWriterOperator and the TableFinishOperator. Thus the multiplexing is needed.
  <p>
  The transferred page layout looks like:
  <p>
  [[row_count_channel], [fragment_channel], [statistic_channel_1] ... [statistic_channel_N]]
  <p>
  [row_count_channel] - contains number of rows processed by a TableWriterOperator instance
  [fragment_channel] - contains arbitrary binary data provided by the ConnectorPageSink#finish for
  the further post processing on the coordinator
  <p>
  [statistic_channel_1] ... [statistic_channel_N] - contain pre-aggregated statistics computed by the
  statistics aggregation operator within the
  TableWriterOperator
  <p>
  Since the final aggregation operator in the TableFinishOperator doesn't know what to do with the
  first two channels, those must be pruned. For the convenience we never set both, the
  [row_count_channel] + [fragment_channel] and the [statistic_channel_1] ... [statistic_channel_N].
  <p>
  If this is a row that holds statistics - the [row_count_channel] + [fragment_channel] will be NULL.
  <p>
  It this is a row that holds the row count or the fragment - all the statistics channels will be set
  to NULL.
  <p>
  Since neither [row_count_channel] or [fragment_channel] cannot hold the NULL value naturally, by
  checking isNull on these two channels we can determine if this is a row that contains statistics.