check null safety

lib/domain/vo/message.dart

@@ -1,15 +1,15 @@
 import 'package:cloud_firestore/cloud_firestore.dart';
 
 class Message {
-  String id;
-  String message;
-  DateTime date;
-  String receiverID;
-  String receiverName;
-  String senderID;
-  String senderName;
-  String messageType;
-  String messageID;
+  String? id;
+  String? message;
+  DateTime? date;
+  String? receiverID;
+  String? receiverName;
+  String? senderID;
+  String? senderName;
+  String? messageType;
+  String? messageID;
 
   Message(
       {this.id,
@@ -21,11 +21,13 @@ class Message {
       this.senderName,
       this.messageType,
       this.messageID});
+
   bool fromToday() {
+    if (date == null) return false;
     var now = DateTime.now();
-    return date.day == now.day &&
-        date.month == now.month &&
-        date.year == now.year;
+    return date!.day == now.day &&
+        date!.month == now.month &&
+        date!.year == now.year;
   }
 
   Map<String, dynamic> toMap() {
@@ -36,9 +38,10 @@ class Message {
   }
 
   bool sameDay(Message another) {
-    return date.year == another.date.year &&
-        date.month == another.date.month &&
-        date.day == another.date.day;
+    if (date == null) return false;
+    return date!.year == another.date!.year &&
+        date!.month == another.date!.month &&
+        date!.day == another.date!.day;
   }
 
   factory Message.fromMap(Map<String, dynamic> map, String id) {
@@ -52,7 +55,7 @@ class Message {
       receiverName: map['receiver_name'],
       messageType: map['msg_type'],
       messageID: map['msg_id'],
-      date: date != null ? date.toDate() : null,
+      date: date.toDate(),
     );
   }
 }