presto-accumulo/src/main/java/io/prestosql/plugin/accumulo/iterators/MaxByteArrayCombiner.java/MaxByteArrayCombiner/reduce
class MaxByteArrayCombiner:    @Override
    public Value reduce(Key key, Iterator<Value> iter)
    {
        Value max = null;
        while (iter.hasNext()) {
            Value test = iter.next();
            if (max == null) {
                max = new Value(test.get());
            }
            else if (comparator.compare(test.get(), max.get()) > 0) {
                max.set(test.get());
            }
        }
        return max;
    }