Integration test search.getTypeHierarchy and make some minor fixes.

pkg/analysis_server/test/search/type_hierarchy_test.dart

Index: pkg/analysis_server/test/search/type_hierarchy_test.dart
diff --git a/pkg/analysis_server/test/search/type_hierarchy_test.dart b/pkg/analysis_server/test/search/type_hierarchy_test.dart
index c0192e0973179dfc6f807e4a6110debe4242e080..a24dd4773d3a8f2d5d4438f221d780ccd7bebe56 100644
--- a/pkg/analysis_server/test/search/type_hierarchy_test.dart
+++ b/pkg/analysis_server/test/search/type_hierarchy_test.dart
@@ -47,7 +47,7 @@ main() {
 ''');
     return waitForTasksFinished().then((_) {
       return _getTypeHierarchy('main() {').then((jsons) {
-        expect(jsons, isEmpty);
+        expect(jsons, isNull);
       });
     });
   }