Invalid use of Null

[CLSkcab]

Frontend: MS Access 2010/VBA
Backend: MS SQL Server 2008

This code is used to determine the the current key (ID) of a table entry. When the table is empty however the following message is issued: Run-time error '94' Invalid use of null. How do I get around this?

Private Sub getID()

Dim OldCaseNum As Integer
OldCaseNum = DMax("ID", "[dbo_BWC]")
 
End Sub

[Rabbit]

Use the Nz() function to change the null to something else.