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

Fixed the errors it threw up.

overlord/src/app/cost-centre/cost-centre-detail/cost-centre-detail.component.ts

@@ -67,7 +67,7 @@ export class CostCentreDetailComponent implements OnInit, AfterViewInit {
 
   getItem(): CostCentre {
     const formModel = this.form.value;
-    this.item.name = formModel.name!;
+    this.item.name = formModel.name ?? '';
     return this.item;
   }
 }