How to change into Version 9 in set Analysis

[#1]

Hi All,

I am having following query as expression in version 8.2 Now i would like to convert this into version 9.But when I tried this not working.Here with I have attached expression.KIndly let mw know how to change.

=if (min(INVOICE_DATE) = max(INVOICE_DATE), INVOICE_DATE,

if (len(min(INVOICE_DATE)) = 0, null(),

date(min(INVOICE_DATE)) & ' / ' & date(max(INVOICE_DATE))))

Thanks & Regards

Jacyn