What Is Wrong With This If..then Statement??

In the following if...then statement, even though the Debug.Print prints a "Null"
the Else part of the statement is executed. Any help is appreciated

Debug.Print Forms!frmReport!txtCustom1
'if id combo box is null then
If Len(Forms!frmReport!txtCustom1) = Null Then
Debug.Print "Then"
'Filter Null strCompanyName records
rst.Filter = "strCompanyName <> """""
Else
Debug.Print "Else"
' filter on portfilio id
rst.Filter = "strJobID = """ & Forms!frmReport!txtCustom1 & """"
End If

Output:
Null
Else