How to Prevent Nulls from Being Written to Database

VWD 2008 Express.  Visual Basic.  SQL Server 2005.

I have formviews that insert records into an SQL database.  A number of the table columns allow Nulls, but I do not want to ever write nulls, as they later cause me problems when I try to read an manipulate the string data.  My question is, "How can I set up my formview insert template so that it never writes Nulls to the SQL database for fields into which the user has not entered data?"  I would prefer that it write blank strings for any fields not entered.  I tried defining the columns in SQL to not allow nulls, and to assign a default of a blank string.  However, the formview still tries to write nulls, and SQL will not allow it.  Thanks for any help.
...