presto-hive/src/main/java/io/prestosql/plugin/hive/RecordFileWriter.java/RecordFileWriter/appendRow
class RecordFileWriter:    public void appendRow(Page dataPage, int position)
    {
        for (int field = 0; field < fieldCount; field++) {
            Block block = dataPage.getBlock(field);
            if (block.isNull(position)) {
                tableInspector.setStructFieldData(row, structFields.get(field), null);
            }
            else {
                setters[field].setField(block, position);
            }
        }

        try {
            recordWriter.write(serializer.serialize(row, tableInspector));
        }
        catch (SerDeException | IOException e) {
            throw new PrestoException(HIVE_WRITER_DATA_ERROR, e);
        }
    }