Lol, ok Rudy.
I don't know the OP is using sprocs (or Stored Procedures/Routines if you prefer), so I should have used a more blanket statement.
Your data access layer will have to handle blank strings for you.
In Microsofts SQL Server there is a function called NullIf() which I would use in this scenario to "convert" blank strings to NULL values. Whether this particular function exists in MySQL is a different question and not one I able to answer at this juncture (dev.mysql just won't load at this location!)