Hi,
I can see that, your project is to fixing bug on SQL Database. There are some changes between MySQL and MariaDB. Thats why you're getting error. There is NO WAY to set default value of every blank field. But this could be done by front-end validation. Or another way is to set a value of every blank field manually. Both of the way will take times, I've to work hard for that.
I've experience of that kind of work as I'm working in company.
It will be nice to work with you. Thanks.