Fix type hierarchy when there is no element.

pkg/analysis_server/lib/src/search/search_domain.dart

 // Copyright (c) 2014, 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 search.domain;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/constants.dart';
@@ skipping 113 matching lines @@
         await searchEngine.searchTopLevelDeclarations(params.pattern);
     _sendSearchNotification(searchId, true, matches.map(toResult));
   }
 
   /**
    * Implement the `search.getTypeHierarchy` request.
    */
   Future getTypeHierarchy(protocol.Request request) async {
     var params = new protocol.SearchGetTypeHierarchyParams.fromRequest(request);
     await server.onAnalysisComplete;
-    // prepare parameters
+    // prepare element
     List<Element> elements =
         server.getElementsAtOffset(params.file, params.offset);
     if (elements.isEmpty) {
       protocol.Response response =
           new protocol.SearchGetTypeHierarchyResult().toResponse(request.id);
       server.sendResponse(response);
+      return;
     }
     Element element = elements.first;
     // prepare type hierarchy
     TypeHierarchyComputer computer = new TypeHierarchyComputer(searchEngine);
     List<protocol.TypeHierarchyItem> items = await computer.compute(element);
     protocol.Response response = new protocol.SearchGetTypeHierarchyResult(
         hierarchyItems: items).toResponse(request.id);
     server.sendResponse(response);
   }
 
@@ skipping 37 matching lines @@
    */
   void _sendSearchResult(protocol.Request request, result) {
     protocol.Response response = result.toResponse(request.id);
     server.sendResponse(response);
   }
 
   static protocol.SearchResult toResult(SearchMatch match) {
     return protocol.newSearchResult_fromMatch(match);
   }
 }