how to replace “?&” to “?” in iis urlrewrite or asp.net mvc route

I am developing the asp.net web api, but the URL format for the client to initiate the request is:

https://xxx.example/abc?&a=1&b=2

How can I change it in Url rewriting of IIS or in the routing rules of the ASP.NET WEB API:

https://xxx.example/abc?a=1&b=2