Merge pull request #139 from dart-lang/remove_nnbd_exclusion

remove a nnbd file exclusion

test/db_all_e2e_test.dart

@@ -1,7 +1,6 @@
 // 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.
-// @dart=2.9
 
 @Tags(['e2e'])
 @Timeout(Duration(seconds: 120))
@@ -26,19 +25,18 @@ Future main() async {
   var now = DateTime.now().millisecondsSinceEpoch;
   var namespace = '${Platform.operatingSystem}$now';
 
-  datastore_impl.DatastoreImpl datastore;
-  db.DatastoreDB datastoreDB;
-  Client client;
+  late datastore_impl.DatastoreImpl datastore;
+  late db.DatastoreDB datastoreDB;
+  Client? client;
 
-  await withAuthClient(scopes, (String project, httpClient) {
+  await withAuthClient(scopes, (String project, httpClient) async {
     datastore = datastore_impl.DatastoreImpl(httpClient, project);
     datastoreDB = db.DatastoreDB(datastore);
     client = httpClient;
-    return null;
   });
 
   tearDownAll(() async {
-    client.close();
+    client?.close();
   });
 
   group('datastore_test', () {