presto-main/src/main/java/io/prestosql/type/UuidType.java/UuidType/getObjectValue
class UuidType:    @Override
    public Object getObjectValue(ConnectorSession session, Block block, int position)
    {
        if (block.isNull(position)) {
            return null;
        }
        return new UUID(block.getLong(position, 0), block.getLong(position, SIZE_OF_LONG)).toString();
    }