Access-VBA: Empty result for missing values in function?

Question

Hi,

I've got a question that probably has a pretty simple answer, but I didn't find a solution yet. Here's an example:

Public Function abc(var_1 As Variant) As Single
abc = 2 * var_1
End Function

I want to call that function in an Access query. Values for 'var_1' are from a numeric (single) data field. Problem: Some the values for var_1 are empty/missing. For those values I need the result of the function to be empty as well, but right now they are '0'.

I tried a lot of things already, but nothing works. The result for empty values is always '0' and not empty. Here's one try:

If IsNull(var_1) Then
        abc = Empty
        Exit Function
End If

Didn't work.

Any help for this problem would be very much appreciated. :)

Edit:

Thanks for the answers. I tried returning a variant before and it did return empty fields. However, the calculated field needs to behave as numberic and not as text, so this solution doesn't work for me. I ended up using the answer of Beth, though it's more work than I'd like to have. ;) Calling the function in SQL:

IIF(IsNull(X)=False;abc(X))

abc in VBA:

Public Function abc(var_1 As Single) As Single
abc = 2 * var_1
End Function

Answer 1

Change the function to look something like the following.

Public Function abc(var_1 As Variant) As Variant
    If IsNumeric(var_1) Then
        abc = 2 * var_1
    Else
        abc = Null
    End If
End Function

I do not believe that you can return a null in a single as you were trying to do.

Answer 2

or test for null at a higher level than the function, although you'll have to do it everywhere the function is called