null safety

lib/pages/invoice/editor/invoice_carton_table.dart

@@ -38,7 +38,7 @@ class InvoiceCartonTable extends StatelessWidget {
         ? [Container()]
         : cartons!.asMap().entries.map((p) {
             return Container(
-              color: p.value.isChecked
+              color: p.value.isChecked!
                   ? Colors.grey.withOpacity(0.2)
                   : Colors.grey.shade50.withOpacity(0.2),
               child: Container(
@@ -56,7 +56,7 @@ class InvoiceCartonTable extends StatelessWidget {
                 child: Row(
                   children: <Widget>[
                     onSelect == null
-                        ? p.value.isChecked
+                        ? p.value.isChecked!
                             ? SizedBox(
                                 child: Icon(Icons.check, color: primaryColor),
                                 width: 30)
@@ -72,7 +72,7 @@ class InvoiceCartonTable extends StatelessWidget {
                       crossAxisAlignment: CrossAxisAlignment.start,
                       children: [
                         Text(
-                          p.value.cartonNumber,
+                          p.value.cartonNumber!,
                           style: textStyle,
                         ),
                       ],

lib/pages/invoice/editor/invoice_discount_list.dart

@@ -68,7 +68,7 @@ class InvoiceDiscountList extends StatelessWidget {
         onSelectChanged: (value) => Navigator.pop(context, c),
         cells: [
           MyDataCell(new Text(
-            c.code,
+            c.code!,
             style: textStyle,
           )),
           MyDataCell(

lib/pages/invoice/editor/invoice_editor.dart

@@ -91,7 +91,7 @@ class _InvoiceEditorState extends State<InvoiceEditor> {
   _loadCartons() async {
     CartonModel cartonModel = Provider.of<CartonModel>(context, listen: false);
     List<Carton> cartons = await cartonModel.getCartonsForInvoice(
-        widget.fcsShipment!.id, widget.customer!.id);
+        widget.fcsShipment!.id!, widget.customer!.id!);
     cartons.forEach((c) {
       c.isChecked = true;
     });
@@ -104,7 +104,7 @@ class _InvoiceEditorState extends State<InvoiceEditor> {
     ShipmentModel shipmentModel =
         Provider.of<ShipmentModel>(context, listen: false);
     List<Shipment> shipments = await shipmentModel.getShipmentWithHandlingFee(
-        widget.fcsShipment!.id, widget.customer!.id);
+        widget.fcsShipment!.id!, widget.customer!.id!);
     shipments.forEach((s) {
       s.isSelected = true;
     });
@@ -117,7 +117,7 @@ class _InvoiceEditorState extends State<InvoiceEditor> {
   _loadDiscount() async {
     DiscountModel discountModel =
         Provider.of<DiscountModel>(context, listen: false);
-    discounts = await discountModel.getDiscount(widget.customer!.id);
+    discounts = (await discountModel.getDiscount(widget.customer!.id!))!;
     if (discounts != null && discounts.length > 0) {
       setState(() {
         _invoice!.discount = discounts.first;
@@ -281,7 +281,7 @@ class _InvoiceEditorState extends State<InvoiceEditor> {
         Column(
           crossAxisAlignment: CrossAxisAlignment.start,
           children: [
-            Text(dateFormatter.format(_invoice!.invoiceDate)),
+            Text(dateFormatter.format(_invoice!.invoiceDate!)),
             SizedBox(
               height: 10,
             ),
@@ -429,7 +429,7 @@ class _InvoiceEditorState extends State<InvoiceEditor> {
       invoice.cargoTypes = cargoTypes;
       invoice.amount = amount;
       invoice.handlingFee = _invoice!.getHandlingFee();
-      invoice.cartons = _invoice!.cartons.where((c) => c.isChecked).toList();
+      invoice.cartons = _invoice!.cartons.where((c) => c.isChecked!).toList();
       invoice.shipments =
           _invoice!.shipments.where((s) => s.isSelected).toList();
       invoice.discount = _invoice!.discount;

lib/pages/invoice/editor/invoice_handling_fee_list.dart

@@ -72,7 +72,7 @@ class InvoiceHandlingFeeList extends StatelessWidget {
         onSelectChanged: (value) => Navigator.pop(context, c),
         cells: [
           MyDataCell(new Text(
-            c.shipmentNumber,
+            c.shipmentNumber!,
             style: textStyle,
           )),
           MyDataCell(