Command Builder

hi, I have filled my datagrid using a dataadapter and i am using a command builder object to update my table back. But if a user deletes any particular cell , (which makes it NULL) , and then if u try clicking the SAVE btn, the command builder throws an error showing " Parameter p1. No size set for variable length data type:String" is there a way in which we can update NULL values back to the database. thanx