It will not save the data if i will leave the column empty

I'm using dbexpress components (SQLConnection, SQLDataSet) and DaTa Access
components(DataSource, DataSource Provider and ClientDataSet). I set up my
EmployeeName, Comments Column on our SQLServer as nvarchar as Data Types.
The problem is, if i will edit the Columns of EmployeeName and comments and
leave it empty it will not save the change that i made. But if i will just
change the data it will save. I checked the EmployeeName and Comment Columns
and made sure it will allow nulls.  It looks like the employeename and
comments column will not allow the column to be empty. How can i fix this