text box value

[connie]

Using Access 2000, I want to toggle between null and a
number in a textbox when I click on a command button.

So, if it's null, set the value to 1. If it's not null,
then make it be null.

This is what I've tried and I have a problem with the line
with the quesion marks. Any suggestions will be
appreciated.

Private Sub cmdSunday_Click()

If Not IsNull(Me.txtSunday.Value) Then
me.txtSunday ?????
Else
TXTSunday = "1"
End If
End Sub