@tojofo I ran a test because your concerns were very valid. It is neccessary as the param string had &null&null&null  
As it is Grails the outcome is very rosy with the existing code.
The println below returns class java.lang.String

def test = {
        def paramsTest = []
        paramsTest.removeAll([null])
        println paramsTest.join('&').class
        render paramsTest
    }