Error occur during report processing

The Hidden expression for the textbox 'Work_order_TABLECAPTION________WorkOderFilter’contains an errror:The qyery returned no rows for the data set.The expression therefore evaluates to null.

On this Expression…

=IIF((Fields!CurrReport_PAGENO.Value = 1)AND(Fields!WorkOrderFilter.value <>nothing),true,false)

Header Section…

CurrReport.SHOWOUTPUT((CurrReport.PAGENO = 1) AND (WorkOrderFilter <> ‘’));