Default Parameter values in SSRS Utility

Hi All,

I've been working on a project to help our marketing team send communications to patrons based upon those patrons demonstrated interests in performances. The method works based upon interest weight, adding up the total weight of all the keywords on future performances for each individual and then sorting the individuals into affinity groups for each future performance. So that the Marketing team would be able to easily make use of this I've built a utility where they can specify parameters of between two and six performances to compare. Then the utility runs and fills tables based upon the patrons greatest affinity among those performances. 

It all WORKS just fine so far. But there's a little hiccup in the experience. When any of the optional performance parameters are left blank the utility doesn't pass the default value of 0 and instead we are presented with feilds for each of the parameters and zeros must be filled in manually. Once those zeros are filled in and we click View report, it works as expected. SO its usable, but any idea how I am losing those default parameters?

Thanks in advance.

Jeff