How can I remove empty fields from my form in the querystring?

I have a simple form with four inputs. When I submit my form, I want to use the GET http method.

For the example :

aaa : foo
bbb : ____
ccc : bar
ddd : ____

I want to have this query string :

/?aaa=foo&ccc=bar

The problem is I have this query string :

/?aaa=foo&bbb=&ccc=bar&ddd=

How can I remove empty fields from my form in the query string ?

Thanks.