How to Create Optional (out of 3 parameters use select value for only 1 parameter)cascading multivalue parameter in SSRS 2008R2

Hi,

I Have 3 multivalue cascading Parameters:

1.CustomerFN

2.CustomerLN

3.CaseID

if I want to make parameter1 and parameter2 optional means if user dont select this two and just select CaseID still user Can view report.

Can I have step by step solution how to make my parameter optional.

I dont want to handle Null or blank.

Replay soon please.

Thank You,

KKP