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

runtime/vm/object.cc

 // Copyright (c) 2012, 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.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 1531 matching lines @@
   OS::Print("%s\n", ToCString());
 }
 
 
 void Object::PrintJSON(JSONStream* stream, bool ref) const {
   if (IsNull()) {
     JSONObject jsobj(stream);
     jsobj.AddProperty("type", ref ? "@Null" : "Null");
     jsobj.AddProperty("id", "objects/null");
     jsobj.AddProperty("valueAsString", "null");
+    if (!ref) {
+      const Class& cls = Class::Handle(this->clazz());
+      jsobj.AddProperty("class", cls);
+      jsobj.AddProperty("size", raw()->Size());
+    }
   } else {
     PrintJSONImpl(stream, ref);
   }
 }
 
 
 RawString* Object::DictionaryName() const {
   return String::null();
 }
 
@@ skipping 18011 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Instance::PrintJSONImpl(stream, ref);
 }
 
 
 }  // namespace dart