null safety

lib/pages/invoice/invoice_list_row.dart

@@ -58,7 +58,9 @@ class InvoiceListRow extends StatelessWidget {
                                 fontSize: 13.0, color: primaryColor),
                           ),
                           new Text(
-                            dateFormatter.format(invoice!.invoiceDate!),
+                            invoice!.invoiceDate != null
+                                ? dateFormatter.format(invoice!.invoiceDate!)
+                                : '',
                             style: new TextStyle(
                                 fontSize: 15.0, color: Colors.grey),
                           )

lib/pages/invoice/invoice_shipment_list_row.dart

@@ -86,7 +86,7 @@ class _InvoiceShipmentListRowState extends State<InvoiceShipmentListRow> {
             ),
             Padding(
               padding: const EdgeInsets.all(0),
-              child: getStatus(_fcsShipment.status!),
+              child: getStatus(_fcsShipment.status??"")
             ),
           ],
         ),