Return 'null' rename refactoring in case of a null element.

pkg/analysis_server/test/services/refactoring/rename_constructor_test.dart

Index: pkg/analysis_server/test/services/refactoring/rename_constructor_test.dart
diff --git a/pkg/analysis_server/test/services/refactoring/rename_constructor_test.dart b/pkg/analysis_server/test/services/refactoring/rename_constructor_test.dart
index a93a01e3795a73a27014fa64f301d34553724e07..9b6d46eedfccfa4e1e8beb5a46fd780ae9801a8d 100644
--- a/pkg/analysis_server/test/services/refactoring/rename_constructor_test.dart
+++ b/pkg/analysis_server/test/services/refactoring/rename_constructor_test.dart
@@ -6,6 +6,7 @@ library test.services.refactoring.rename_constructor;
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/services/correction/status.dart';
+import 'package:analysis_server/src/services/refactoring/refactoring.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
@@ -199,6 +200,11 @@ main() {
 ''');
   }
 
+  void test_newInstance_nullElement() {
+    RenameRefactoring refactoring = new RenameRefactoring(searchEngine, null);
+    expect(refactoring, isNull);
+  }
+
   void _createConstructorDeclarationRefactoring(String search) {
     ConstructorElement element = findNodeElementAtString(
         search, (node) => node is ConstructorDeclaration);