CRM 2015 Online FetchXml based SSRS report

Hi Team,

I have to develop one custom SSRS report for crm online. as per requirement, there are 3 parameters in report with multi select options. One multi select parameter is mandatory , while other 2 are optional. problem is , when I keep parameter as multi select in ssrs report, all three parameter becomes mandatory. kindly suggest how to make multi select parameter as optional.

Thanks

Aarush