Thank you so much for your reply.
This report has no dataItem it is just for processing
I solved it by validating on trigger QueryClosedPage of request page like below
trigger OnQueryClosePage(CloseAction: Action): Boolean
var
begin
if (CloseAction = Action::OK) or (format(CloseAction) = 'Schedule') then begin
if (gCatVendorNo = '') then
Error('Please select the vendor catalog');
if (gPriceValidDate = 0D) then
Error('Please select the Valid Pricce date');
end
end;