Try to retain original structure of URI.

tests/corelib/uri_query_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import "package:expect/expect.dart";
 
 void testInvalidArguments() {
 }
 
 void testEncodeQueryComponent() {
   // This exact data is from posting a form in Chrome 26 with the one
   // exception that * is encoded as %30 and ~ is not encoded as %7E.
   Expect.equals(
       "%21%22%23%24%25%26%27%28%29%2A%2B%2C-.%2F%"
       "3A%3B%3C%3D%3E%3F%40%5B%5C%5D%5E_%60%7B%7C%7D~",
       Uri.encodeQueryComponent("!\"#\$%&'()*+,-./:;<=>?@[\\]^_`{|}~"));
   Expect.equals("+%2B+", Uri.encodeQueryComponent(" + "));
   Expect.equals("%2B+%2B", Uri.encodeQueryComponent("+ +"));
 }
 
 void testQueryParameters() {
   test(String query, Map<String, String> parameters, [String normalizedQuery]) {
     if (normalizedQuery == null) normalizedQuery = query;
     check(uri) {
       Expect.equals(normalizedQuery, uri.query);
-      if (query.isEmpty) {
-        Expect.equals(normalizedQuery, uri.toString());
-      } else {
-        Expect.equals("?$normalizedQuery", uri.toString());
-      }
+      Expect.equals("?$normalizedQuery", uri.toString());
       if (parameters.containsValue(null)) {
         var map = new Map.from(parameters);
         map.forEach((k, v) { if (v == null) map[k] = ""; });
         Expect.mapEquals(map, uri.queryParameters);
       } else {
         Expect.mapEquals(parameters, uri.queryParameters);
       }
     }
 
     var uri1 = new Uri(queryParameters: parameters);
@@ skipping 129 matching lines @@
   test(new Uri(queryParameters: {"a": "b", "c": "d"}).queryParameters);
 }
 
 main() {
   testInvalidArguments();
   testEncodeQueryComponent();
   testQueryParameters();
   testInvalidQueryParameters();
   testQueryParametersImmutableMap();
 }