Display a message "No data avalaible for period xy"

Hi folks,

I have a report where the user is prompted to enter a date via a BW variable. Then a small time series is shown in report with the entered date and 90days before(e.g. 31.12., 31.03). Sometimes there is no data for a date.

Can I build a formula which lets display a message like "No data for 31.12."?

I tried this:

While {date_field} <= {?parameter} do

if Isnull({key_figure)

then {date_field}

But the formula gives an error.

Anyone a different idea?

Thank you very much!