Sqlite3 not setting default attributes to nil?

Hi.
I’m using mysql for my development database and sqlite3 for testing,
problem is, none of my unit tests validations are working because
rather than setting attributes to nil by default, sqlite3 seems to be
setting strings to empty string and numeric attributes to 0!!?

Any way to stop SQLite3 from handling null values like this? Is it a
defect in rails?