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

runtime/bin/vmservice/observatory/lib/src/elements/inbound_reference.html

 <link rel="import" href="../../../../packages/polymer/polymer.html">
 <link rel="import" href="curly_block.html">
 <link rel="import" href="observatory_element.html">
 <link rel="import" href="service_ref.html">
 
 <polymer-element name="inbound-reference" extends="service-ref">
   <template>
     <link rel="stylesheet" href="css/shared.css">
-    <style>
-      .errorBox {
-        background-color: #f5f5f5;
-        border: 1px solid #ccc;
-        padding: 10px;
-        font-family: consolas, courier, monospace;
-        font-size: 1em;
-        line-height: 1.2em;
-        white-space: pre;
-      }
-    </style>
     <div>
       from <any-service-ref ref="{{ source }}"></any-service-ref>
       <template if="{{ slotIsArrayIndex }}">via [{{ slot }}]</template>
       <template if="{{ slotIsField }}">via <field-ref ref="{{ slot }}"></template>
 
       <curly-block callback="{{ expander() }}">
         <div class="memberList">
           <div class="memberItem">
             <div class="memberName">
               <template repeat="{{ reference in inboundReferences] }}">
                 <inbound-reference ref="{{ reference }}"></inbound-reference>
               </template>
             </div>
           </div>
         </div>
       </curly-block>
     </div>
   </template>
 </polymer-element>
 
 <script type="application/dart" src="inbound_reference.dart"></script>