presto-main/src/main/java/io/prestosql/util/JsonUtil.java/JsonUtil/addIfAbsent
class JsonUtil:        public boolean addIfAbsent(int position)
        {
            checkArgument(position >= 0, "position is negative");
            int hashPosition = getHashPosition(position);
            if (positionByHash[hashPosition] == EMPTY_SLOT) {
                positionByHash[hashPosition] = position;
                size++;
                if (size >= maxFill) {
                    rehash();
                }
                return true;
            }
            else {
                return false;
            }
        }