SSRS - Checking whether the data is null

I've the following expression in my report. ``` =FormatNumber(MAX(Fields!Reading.Value, "CellReading_Reading"),3) ``` Now when the dataset is empty 'Fields!Reading.Value' becomes empty and finding their maximum is invalid. How can i check if the entire column is empty? I tried the following with no luck. ``` =iif(IsNothing(Fields!.Reading.Value),"",FormatNumber(MAX(Fields!Reading.Value, "CellReading_Reading"),3)) ``` But still i'm getting #Error in the report. I also checked out link and was not able to get a clue from it. I want to handle it in the report level.