Stuck, Please Give it a look

I have some invoice numbers (which is a string) pulling from an SQL database using an adodc control. Some of the invoices that are in the database are blank. I can't figure out how to check and make all the invoice numbers that are blank to be changed to a zero. here's what i tried

Do while adodc1.recordset.Eof = false Then
If adodc1.recordset.Invoice_no = "" '(I tried Null also)
adodc1.recordset.Invoice_no = "0"
End if
Loop

**I'm still new to using databases and the adodc

Thanks

Use

If IsNull(adodc1.recordset.Invoice_no) then...