Switched on the @typescript-eslint/no-non-null-assertion rule in eslint.

Fixed the errors it threw up.

overlord/src/app/closing-stock/closing-stock.component.ts

@@ -118,7 +118,7 @@ export class ClosingStockComponent implements OnInit {
     this.info.date = moment(formModel.date).format('DD-MMM-YYYY');
     const array = this.form.controls.stocks;
     this.info.items.forEach((item, index) => {
-      item.physical = +array.controls[index].value.physical!;
+      item.physical = +(array.controls[index].value.physical ?? '');
       item.costCentre =
         array.controls[index].value.costCentre == null
           ? undefined
@@ -132,7 +132,7 @@ export class ClosingStockComponent implements OnInit {
 
     return new ClosingStock({
       date: moment(formModel.date).format('DD-MMM-YYYY'),
-      costCentre: new CostCentre({ id: formModel.costCentre! }),
+      costCentre: new CostCentre({ id: formModel.costCentre ?? '' }),
     });
   }