null safety

lib/pages/carton/cargo_table.dart

@@ -6,10 +6,10 @@ import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
 
 class CargoTable extends StatefulWidget {
-  final List<CargoType> cargoTypes;
+  final List<CargoType>? cargoTypes;
 
   const CargoTable({
-    Key key,
+    Key? key,
     this.cargoTypes,
   }) : super(key: key);
 
@@ -58,13 +58,13 @@ class _CargoTableState extends State<CargoTable> {
       return [];
     }
     double total = 0;
-    var rows = widget.cargoTypes.map((c) {
-      total += c.weight;
+    var rows = widget.cargoTypes!.map((c) {
+      total += c.weight!;
       return MyDataRow(
         onSelectChanged: (bool selected) async {},
         cells: [
           MyDataCell(new Text(
-            c.name == null ? "" : c.name,
+            c.name ?? "",
             style: textStyle,
           )),
           MyDataCell(c.qty == null || c.qty == 0
@@ -81,7 +81,7 @@ class _CargoTableState extends State<CargoTable> {
                   ),
                 )),
           MyDataCell(
-            Text(c.weight == null ? "0" : c.weight.toStringAsFixed(2),
+            Text(c.weight == null ? "0" : c.weight!.toStringAsFixed(2),
                 style: textStyle),
           ),
         ],