problem in testing for Null in If-Else

[Guest_imported]

Hi,

Something wrong with testing for Null value?

==================================
If Cust_name = Null then

msgbox "No name!"
End if
====================================

Cannot work even i can be sure than Cust_name is Null

 

[danvlas]

If IsNull(Cust_name) then

msgbox "No name!"
End if

or, to test for Null OR a zero-length string:

If Len(Nz(Cust_name, "&quot) = 0 Then
MsgBox "no name!"
End If

Dan

 

[DonQuichote]

What you encountered is called "Null propagation". Microsoft introduced it as a feature, but I think it is a severe bug. It means that if Null is input to a function or even operator, Null is the output also.

So the '=' operator is NOT a boolean, but a variant:

Null = Null,
(Cust_name = Null) = Null

, not true, neither false!

But

if Null then...

is executed as

if False then...

Nicest problem:

(not false) = true

, but

(not Null)

remains

Null

...

That is why you need the

IsNull()

function

Best regards