A multi select parameter in Report is not allowing a null value.

My dear Axaptians, I hope you all are having a great day. Jumping straight to the point. I am stuck somewhere. I have created a multi select parameter on a report, AX 2012. The multiselect parameter is working perfectly fine, except, it is not allowing me to pass a blank value. If I leave it blank, the report throws an error " parameter is missing a value". I tried to set the properties in VS also. When I try setting Allow Blank: True and Nullable: True, the report does not deploy in VS. It throws an error, that a multiselect parameter cannot be null. Can somebody please help me in fixing this ? You can just answer with a url link also, if you may have come across anything related to this.Thanks so much in advance guys.