presto-main/src/main/java/io/prestosql/operator/aggregation/SumDataSizeForStats.java/SumDataSizeForStats/update
class SumDataSizeForStats:    private static void update(NullableLongState state, long size)
    {
        if (state.isNull()) {
            state.setNull(false);
            state.setLong(size);
        }
        else {
            state.setLong(state.getLong() + size);
        }
    }