Fix type hierarchy when there is no element.

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

Index: pkg/analysis_server/lib/src/search/search_domain.dart
diff --git a/pkg/analysis_server/lib/src/search/search_domain.dart b/pkg/analysis_server/lib/src/search/search_domain.dart
index 8f550b60b99cef832ed95abbba600c8da37b09f3..01fd53e49a6bee29d928de7ee54af0ef088d8b04 100644
--- a/pkg/analysis_server/lib/src/search/search_domain.dart
+++ b/pkg/analysis_server/lib/src/search/search_domain.dart
@@ -131,13 +131,14 @@ class SearchDomainHandler implements protocol.RequestHandler {
   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