How can i Ignore optional parameter in Web Method call

I am trying to call web method without optional parameter value via HTTP Get method. but by doing so i get error like

There is three parameter in my web method call Name,BirthDate1 and Birthdate2

If I have called web service by below URL

http://localhost:3933/ChartWheelWebservice/service.asmx/WheelChart?Name=adday&Date=12-05-1960&Date2=12-05-1960, then its work fine

but if i remove parameter name from URL like

http://localhost:3933/ChartWheelWebservice/service.asmx/WheelChart?Date=12-05-1960&Date2=12-05-1960, then i get below error
System.InvalidOperationException: Missing parameter: Name.
at System.Web.Services.Protocols.ValueCollectionParamete ...