presto-main/src/main/java/io/prestosql/operator/aggregation/minmaxby/SliceAndBlockPositionStateSerializer.java/SliceAndBlockPositionStateSerializer/readFirstField
class SliceAndBlockPositionStateSerializer:    @Override
    void readFirstField(Block block, int position, SliceAndBlockPositionValueState state)
    {
        state.setFirst(firstType.getSlice(block, position));
    }