Rewrite function breaks multiple parameters

Using a rewrite rule on a view with multiple parameters doesn't work as the resulting URL seems to be missing ampersands between the parameters. When using the _design document below and a URL like http://localhost:5984/database_name/_design/test/_rewrite/views/_view/view_name the following error occurs:

{"error":"query_parse_error","reason":"Invalid boolean parameter: \"truekey=null\""}

Minimal _design document:
{
"_id": "_design/test",
"language": "javascript",
"rewrites": "function(req) {return {path: '../'+req.path.slice(4).join('/'),query:

}};"
}

Couchdb version: v. 2.0.0