Start to fix null safety migration errors

lib/helpers/serialization/base_serialization_helper.dart

@@ -17,7 +17,7 @@ abstract class SerializableElement<T> extends Comparable<T> {
 
 abstract class BaseSerializationHelper<T extends SerializableElement> {
   /// List cache
-  List<T> _cache;
+  List<T>? _cache;
 
   /// The name of the type of data to serialise
   String get type;
@@ -48,12 +48,15 @@ abstract class BaseSerializationHelper<T extends SerializableElement> {
     try {
       final file = await _getFilePath();
 
-      if (!await file.exists()) return _cache = [];
+      if (!await file.exists()) {
+        _cache = [];
+        return;
+      }
 
       final List<dynamic> json = jsonDecode(await file.readAsString());
       _cache = json.cast<Map<String, dynamic>>().map(parse).toList();
 
-      _cache.sort();
+      _cache!.sort();
     } catch (e, s) {
       logError(e, s);
       print("Failed to read serialized data!");
@@ -67,8 +70,10 @@ abstract class BaseSerializationHelper<T extends SerializableElement> {
 
     try {
       final file = await _getFilePath();
-      await file.writeAsString(jsonEncode(
-          _cache.map((e) => e.toJson()).toList().cast<Map<String, dynamic>>()));
+      await file.writeAsString(jsonEncode(_cache!
+          .map((e) => e.toJson())
+          .toList()
+          .cast<Map<String, dynamic>>()));
     } catch (e, s) {
       print("Failed to write file!");
       logError(e, s);
@@ -78,7 +83,7 @@ abstract class BaseSerializationHelper<T extends SerializableElement> {
   /// Get the current list of elements
   Future<List<T>> getList() async {
     await _loadCache();
-    return List.from(_cache);
+    return List.from(_cache!);
   }
 
   /// Set a new list of conversations
@@ -90,23 +95,23 @@ abstract class BaseSerializationHelper<T extends SerializableElement> {
   /// Insert new element
   Future<void> insert(T el) async {
     await _loadCache();
-    _cache.add(el);
-    _cache.sort();
+    _cache!.add(el);
+    _cache!.sort();
     await _saveCache();
   }
 
   /// Insert new element
   Future<void> insertMany(List<T> els) async {
     await _loadCache();
-    _cache.addAll(els);
-    _cache.sort();
+    _cache!.addAll(els);
+    _cache!.sort();
     await _saveCache();
   }
 
   /// Check if any entry in the last match the predicate
   Future<bool> any(bool isContained(T t)) async {
     await _loadCache();
-    return _cache.any((element) => isContained(element));
+    return _cache!.any((element) => isContained(element));
   }
 
   Future<bool> has(T el) => any((t) => t == el);
@@ -114,7 +119,7 @@ abstract class BaseSerializationHelper<T extends SerializableElement> {
   /// Check if any entry in the last match the predicate
   Future<T> first(bool filter(T t)) async {
     await _loadCache();
-    return _cache.firstWhere((element) => filter(element));
+    return _cache!.firstWhere((element) => filter(element));
   }
 
   /// Replace an element with another one
@@ -122,10 +127,10 @@ abstract class BaseSerializationHelper<T extends SerializableElement> {
     await _loadCache();
 
     // Insert or replace the element
-    _cache = _cache.where((element) => !isToReplace(element)).toList();
-    _cache.add(newEl);
+    _cache = _cache!.where((element) => !isToReplace(element)).toList();
+    _cache!.add(newEl);
 
-    _cache.sort();
+    _cache!.sort();
     await _saveCache();
   }
 
@@ -133,8 +138,8 @@ abstract class BaseSerializationHelper<T extends SerializableElement> {
   Future<void> insertOrReplaceElements(List<T> list) async {
     await _loadCache();
 
-    _cache.removeWhere((element) => list.any((newEl) => element == newEl));
-    _cache.addAll(list);
+    _cache!.removeWhere((element) => list.any((newEl) => element == newEl));
+    _cache!.addAll(list);
 
     await _saveCache();
   }
@@ -142,7 +147,7 @@ abstract class BaseSerializationHelper<T extends SerializableElement> {
   /// Remove elements
   Future<void> removeElement(bool isToRemove(T t)) async {
     await _loadCache();
-    _cache.removeWhere((element) => isToRemove(element));
+    _cache!.removeWhere((element) => isToRemove(element));
     await _saveCache();
   }
 

lib/helpers/serialization/conversation_message_serialization_helper.dart

@@ -8,7 +8,7 @@ import 'package:comunic/models/conversation_message.dart';
 ///
 /// @author Pierre Hubert
 
-HashMap<int, ConversationsMessagesSerializationHelper> _instances;
+HashMap<int?, ConversationsMessagesSerializationHelper>? _instances;
 
 class ConversationsMessagesSerializationHelper
     extends BaseSerializationHelper<ConversationMessage> {
@@ -18,13 +18,13 @@ class ConversationsMessagesSerializationHelper
       : convID = convID,
         assert(convID != null);
 
-  factory ConversationsMessagesSerializationHelper(int convID) {
+  factory ConversationsMessagesSerializationHelper(int? convID) {
     if (_instances == null) _instances = HashMap();
 
-    if (!_instances.containsKey(convID))
-      _instances[convID] = ConversationsMessagesSerializationHelper._(convID);
+    if (!_instances!.containsKey(convID))
+      _instances![convID] = ConversationsMessagesSerializationHelper._(convID!);
 
-    return _instances[convID];
+    return _instances![convID]!;
   }
 
   @override

lib/helpers/serialization/conversations_serialization_helper.dart

@@ -28,5 +28,5 @@ class ConversationsSerializationHelper
       ConversationsList()..addAll(await super.getList());
 
   /// Get a conversation
-  Future<Conversation> get(int id) => first((t) => t.id == id);
+  Future<Conversation> get(int? id) => first((t) => t.id == id);
 }

lib/helpers/serialization/user_list_serialization_helper.dart

@@ -5,7 +5,7 @@ import 'package:comunic/models/user.dart';
 ///
 /// @author Pierre Hubert
 
-UsersListSerialisationHelper _singleton;
+UsersListSerialisationHelper? _singleton;
 
 class UsersListSerialisationHelper extends BaseSerializationHelper<User> {
   UsersListSerialisationHelper._();
@@ -13,7 +13,7 @@ class UsersListSerialisationHelper extends BaseSerializationHelper<User> {
   factory UsersListSerialisationHelper() {
     if (_singleton == null) _singleton = UsersListSerialisationHelper._();
 
-    return _singleton;
+    return _singleton!;
   }
 
   @override
@@ -23,6 +23,6 @@ class UsersListSerialisationHelper extends BaseSerializationHelper<User> {
   User parse(Map<String, dynamic> m) => User.fromJson(m);
 
   /// Remove a user by its ID
-  Future<void> removeUserByID(int userID) =>
+  Future<void> removeUserByID(int? userID) =>
       removeElement((t) => t.id == userID);
 }