Make plugin able to override values only if they don't exist already

[NogaMan]

Currently there is no way to add query params to url only when a parameter with the same name already exist.
My case:
In my project "noredirect" param is always added to the url, but for some testcases I need to test redirects, so when I call this.browser.url() with an url containing &noredirect=0, it gets concatenated and I get ...&noredirect=0&noredirect=1, which breaks the logic