Grid advanced search NOT EMPTY returns all rows but only some have values

I have a string field in a mysql database with 600 rows having the value ‘Y’ and the rest are blank (’’). Advanced Search incorrectly returns all rows when NOT EMPTY is selected. Of course, all rows are returned if search is set to EMPTY. No rows are NULL. Other than searching for a specific value such as ‘Y’, is there another way to get the non-empty rows?