presto-orc/src/main/java/io/prestosql/orc/writer/MapColumnWriter.java/MapColumnWriter/getColumnStripeStatistics
class MapColumnWriter:    @Override
    public Map<OrcColumnId, ColumnStatistics> getColumnStripeStatistics()
    {
        checkState(closed);
        ImmutableMap.Builder<OrcColumnId, ColumnStatistics> columnStatistics = ImmutableMap.builder();
        columnStatistics.put(columnId, ColumnStatistics.mergeColumnStatistics(rowGroupColumnStatistics));
        columnStatistics.putAll(keyWriter.getColumnStripeStatistics());
        columnStatistics.putAll(valueWriter.getColumnStripeStatistics());
        return columnStatistics.build();
    }