Hide field from Tablix based on query field valu

Hi,I have a report where there are fields like Field1,Field2,Field3,Field4 etc . In the report query there is a field named IsParentAccount . If it is 0 then I need to hide Field4 from the dataset else if IsParentAcoount = 1 then Show Field4 . I am using expression=IIF(Fields!IsParentaccount.Value.Equals(1),False,True) in the hidden expression for this field . When no rows returned for this dataset then I get an error ."The Hidden expression for the tectbox 'Textbox6' contains an error:Object reference not set to an instance of an object "Please helpThanks,PSB