How to offer user choice of params

We have for our items, what we call Reporting Category codes. This is more description about the item. we have 15 of these.

One report was only had RC9 as a param. Now they would like to have all 15. However, they would like to choose

say RC1 or RC3. Or some combo but not all 15.

the issue is that not all items have any RC data. In that case, it does not show any data at all.

I did this params as Optional Prompt = True but it is still processing it I beleive. because I got no data results.

If I have to make a front end that is ok, but I am missing something in this? If i offer 15 rc's and they dont pass any of the data values on some

can this be ignored? and show data based on the rc's they do enter values?