Issue with Determining when Checkbox is Null

Hi,

I have a routine that set the value of a particular checkbox to "Null." Later on, I'm using an if statement to evalute if the value of the checkbox is NOT false (meaning a null value should pass the logic test). However, whenever this logic is evaluated, it does not pass the test. For example:

 Private Sub CommandButton1_Click
CheckBox1 = Null
End Sub

Then later,

 If CheckBox1 <> False Then
range("a1") = "Test"
End if

I would expect that when the If statement is evaluated after CommandButton1 has been clicked, Range A1 would say "Test," but it never does... Help?