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

runtime/bin/vmservice/observatory/lib/src/elements/service_ref.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_ref_element;
 
 import 'dart:html';
 import 'package:logging/logging.dart';
 import 'package:polymer/polymer.dart';
 import 'observatory_element.dart';
@@ skipping 68 matching lines @@
         element.ref = ref;
         return element;
       case 'Function':
         ServiceRefElement element = new Element.tag('function-ref');
         element.ref = ref;
         return element;
       case 'Library':
         ServiceRefElement element = new Element.tag('library-ref');
         element.ref = ref;
         return element;
-      case 'Type':
       case 'Array':
+      case 'Bigint':
       case 'Bool':
       case 'Closure':
       case 'Double':
       case 'GrowableObjectArray':
       case 'Instance':
+      case 'Mint':
+      case 'Null':
       case 'Smi':
-      case 'Mint':
-      case 'Bigint':
       case 'String':
+      case 'Type':
         ServiceRefElement element = new Element.tag('instance-ref');
         element.ref = ref;
         return element;
       default:
         SpanElement element = new Element.tag('span');
         element.text = "<<Unknown service ref: $ref>>";
         return element;
     }
   }
 
   refChanged(oldValue) {
     // Remove the current view.
     children.clear();
     if (ref == null) {
       Logger.root.info('Viewing null object.');
       return;
     }
     var type = ref.serviceType;
     var element = _constructElementForRef();
     if (element == null) {
       Logger.root.info('Unable to find a ref element for \'${type}\'');
       return;
     }
     children.add(element);
     Logger.root.info('Viewing object of \'${type}\'');
   }
 }