Fix for specifying querystring without extra params

The bug was introduced in the move to ring-codec as the nil
behaviour differed in form-encode

src/ring/mock/request.clj

@@ -9,7 +9,8 @@
 (defn- encode-params
   "Turn a map of parameters into a urlencoded string."
   [params]
-  (codec/form-encode params))
+  (if params
+    (codec/form-encode params)))
 
 (defn header
   "Add a HTTP header to the request map."

test/ring/mock/test/request.clj

@@ -35,6 +35,9 @@
       (is (= (slurp body) "quux=zot"))))
   (testing "nil path"
     (is (= (:uri (request :get "http://example.com")) "/")))
+  (testing "only params in :get"
+    (is (= (:query-string (request :get "/?a=b"))
+           "a=b")))
   (testing "added params in :get"
     (is (= (:query-string (request :get "/" (array-map :x "y" :z "n")))
            "x=y&z=n"))