Treat null like the object it is in the Observatory and Service.

runtime/bin/vmservice/observatory/lib/src/elements/service_view.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.
 
 library service_object_view_element;
 
 import 'dart:html';
 import 'package:logging/logging.dart';
 import 'package:observatory/service.dart';
 import 'package:observatory/tracer.dart';
@@ skipping 70 matching lines @@
         // reasonable way.
       case 'Type':
       case 'Array':
       case 'Bool':
       case 'Closure':
       case 'Double':
       case 'GrowableObjectArray':
       case 'Instance':
       case 'Smi':
       case 'Mint':
+      case 'Null':
       case 'Bigint':
       case 'String':
         InstanceViewElement element = new Element.tag('instance-view');
         element.instance = object;
         return element;
       case 'IO':
         IOViewElement element = new Element.tag('io-view');
         element.io = object;
         return element;
       case 'HttpServerList':
@@ skipping 153 matching lines @@
 
   dynamic expander() {
     return expandEvent;
   }
 
   void expandEvent(bool exp, var done) {
     expand = exp;
     done();
   }
 }