Error by inserting a Date - DataSet

[Carlos A.]

Hello all
(VB - SQL Server 2005)
I create a DataSet with the insert, update, fill... functions.
I have a problem when I try to insert a DateTime field only when it's empty,
I have the error message:
It's not possible to convert string to Date.
Normally when CustomerDate is not empty I convert the value with Cdate( ).
My question is: How can I insert a empty value in this field?

Thanks a lot