migrated local_settings to null safety

lib/utils/local_settings.dart

@@ -1,5 +1,3 @@
-// @dart=2.9
-
 import 'package:shared_preferences/shared_preferences.dart';
 
 enum AlbumSortKey {
@@ -13,15 +11,14 @@ class LocalSettings {
 
   static final LocalSettings instance = LocalSettings._privateConstructor();
   static const kCollectionSortPref = "collection_sort_pref";
-  SharedPreferences _prefs;
+  late SharedPreferences _prefs;
 
   Future<void> init() async {
     _prefs = await SharedPreferences.getInstance();
   }
 
   AlbumSortKey albumSortKey() {
-    return AlbumSortKey.values[_prefs.getInt(kCollectionSortPref) ?? 0] ??
-        AlbumSortKey.lastUpdated;
+    return AlbumSortKey.values[_prefs.getInt(kCollectionSortPref) ?? 0];
   }
 
   Future<bool> setAlbumSortKey(AlbumSortKey key) {