How to prevent parameter error for NULL dataset?

I developed an RDL file with a parameter set to be the field value, named "Client", of one of my datasets.  I use this parameter value in the page footer because this was the only way I could get Client to appear correctly in the footer.  The other methods Client value did not always appear correctly.

Here is what this parameter properties look like:

So this works if there is data, however, if there are no records in rpt_rd_RecreationTherapy, then I get the following error:

and in my page footer, I have a text box set to the following:

=iif(isnothing(Parameters!new_youth.Value),"",Parameters!new_youth.Value)

Ryan D