null safety

lib/domain/entities/cargo_type.dart

@@ -1,17 +1,17 @@
 class CargoType {
-  String id;
-  String name;
-  double rate;
-  double weight;
-  bool isChecked;
-  int qty;
-  bool isCutomDuty;
-  double customDutyFee;
+  String? id;
+  String? name;
+  double? rate;
+  double? weight;
+  bool? isChecked;
+  int? qty;
+  bool? isCutomDuty;
+  double? customDutyFee;
 
   double get calAmount => (calRate ?? 0) * (calWeight ?? 0);
 
-  double calRate;
-  double calWeight;
+  double? calRate;
+  double? calWeight;
   CargoType(
       {this.id,
       this.name,
@@ -52,7 +52,7 @@ class CargoType {
   }
 
   CargoType clone() {
-    return CargoType.fromMap(toMap(), this.id);
+    return CargoType.fromMap(toMap(), this.id!);
   }
 
   @override
@@ -63,7 +63,7 @@ class CargoType {
 
   @override
   String toString() {
-    return name;
+    return name!;
   }
 
   bool isChangedForEdit(CargoType cargoType) {