Unexpected Results when Using ROUND()

[suyZhong]

Consider the test case below. The result of the query is different from MySQL.

SELECT ROUND('');
-- MySQL: 0
-- Dolt: Empty set

Besides, it would cause below query return an unexpected result.

SELECT 1 WHERE (ROUND('')) UNION ALL SELECT 1 WHERE (NOT (ROUND(''))) UNION ALL SELECT 1 WHERE ((ROUND('')) IS NULL);
-- Expected: 1
-- Actual: Empty set

I originally find this by building dolt from source code 3c8cc08

[max-hoffman]

Thanks! Tagging @jycor for visibility, might not get to this one until next week because of the New Year.