check null safety

lib/domain/entities/processing.dart

@@ -1,15 +1,15 @@
 import 'package:fcs/domain/entities/package.dart';
 
 class Processing {
-  String id;
+  String? id;
   //for consignee
-  String userID;
-  String userName;
-  String userPhoneNumber;
+  String? userID;
+  String? userName;
+  String? userPhoneNumber;
   //for shipper
-  String fcsID;
-  String shipperName;
-  String shipperPhoneNumber;
+  String? fcsID;
+  String? shipperName;
+  String? shipperPhoneNumber;
 
   List<Package> packages;
 
@@ -21,7 +21,7 @@ class Processing {
       this.fcsID,
       this.shipperName,
       this.shipperPhoneNumber,
-      this.packages});
+      this.packages = const []});
 
   @override
   bool operator ==(Object other) => other is Processing && other.id == id;