Misc service fixes

runtime/vm/service/message.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.
 
 part of vmservice;
 
 class Message {
   final Completer _completer = new Completer.sync();
   bool get completed => _completer.isCompleted;
   /// Future of response.
@@ skipping 18 matching lines @@
     pathSegments.forEach((String segment) {
       if (segment == null || segment == '') {
         return;
       }
       path.add(segment);
     });
   }
 
   Message.fromJsonRpc(this.client, Map map)
       : serial = map['id'], method = map['method'] {
-    params.addAll(map['params']);
+    if (map['params'] != null) {
+      params.addAll(map['params']);
+    }
   }
 
   static String _methodNameFromUri(Uri uri) {
     if (uri == null) {
       return '';
     }
     if (uri.pathSegments.length == 0) {
       return '';
     }
     return uri.pathSegments[0];
@@ skipping 103 matching lines @@
     };
     _completer.complete(JSON.encode(response));
   }
 }
 
 bool sendIsolateServiceMessage(SendPort sp, List m)
     native "VMService_SendIsolateServiceMessage";
 
 void sendRootServiceMessage(List m)
     native "VMService_SendRootServiceMessage";