check null safety

lib/pages/carton/carton_cargo_table.dart

@@ -33,7 +33,7 @@ class _CargoTableState extends State<CargoTable> {
     cargoTypes = widget.cargoTypes;
     if (!widget.isNew!) {
       totalWeight =
-          cargoTypes!.fold(0, (previous, current) => previous + current.weight!);
+          cargoTypes!.fold(0, (previous, current) => previous + current.weight);
     }
 
     super.initState();
@@ -42,7 +42,7 @@ class _CargoTableState extends State<CargoTable> {
   @override
   Widget build(BuildContext context) {
     print("Cargotypes:${cargoTypes!.length}");
-    
+
     return SingleChildScrollView(
       scrollDirection: Axis.horizontal,
       child: MyDataTable(
@@ -86,7 +86,7 @@ class _CargoTableState extends State<CargoTable> {
         cells: [
           MyDataCell(
             new Text(
-              c.name ??'',
+              c.name ?? '',
               style: textStyle,
             ),
           ),
@@ -144,7 +144,7 @@ class _CargoTableState extends State<CargoTable> {
                         context: context,
                         builder: (_) => DialogInput(
                             label: "cargo.weight",
-                            value: c.weight!.toStringAsFixed(2)));
+                            value: c.weight.toStringAsFixed(2)));
 
                     if (_t == null) return;
                     setState(() {
@@ -162,7 +162,7 @@ class _CargoTableState extends State<CargoTable> {
                       borderRadius: BorderRadius.all(Radius.circular(5.0)),
                     ),
                     child: Text(
-                        c.weight == null ? "0.00" : c.weight!.toStringAsFixed(2),
+                        c.weight == null ? "0.00" : c.weight.toStringAsFixed(2),
                         style: textStyle),
                   ),
                 ),
@@ -252,11 +252,10 @@ class _CargoTableState extends State<CargoTable> {
 }
 
 CargoType? autoCalWeight(List<CargoType> cargoTypes, double total) {
-  if ((cargoTypes?.length ?? 0) == 0 || total == 0) return null;
   List<CargoType> noWeight = cargoTypes.where((c) => c.weight == 0).toList();
   if (noWeight.length != 1) return null;
 
-  var _existing =
+  double _existing =
       cargoTypes.fold(0, (previous, current) => previous + current.weight);
 
   noWeight[0].weight = total - _existing;