presto-orc/src/main/java/io/prestosql/orc/writer/ByteColumnWriter.java/ByteColumnWriter/finishRowGroup
class ByteColumnWriter:    @Override
    public Map<OrcColumnId, ColumnStatistics> finishRowGroup()
    {
        checkState(!closed);
        ColumnStatistics statistics = new ColumnStatistics((long) nonNullValueCount, 0, null, null, null, null, null, null, null, null);
        rowGroupColumnStatistics.add(statistics);
        nonNullValueCount = 0;
        return ImmutableMap.of(columnId, statistics);
    }