What do you mean by never set? In the database, you can either enter a string (empty or non-empty) or NULL in a column. There no such thing called never set.

That's my question, if you have a field that represents something and that field is a string that can be empty, null or contains anny string, if you don't use NULL how do you make the difference between an empty string and a null string ( user set "" vs never set anything )