Angular2 conditional subscription to route param

transaction.component.html

<my-transaction-form [transaction]="pageTransaction$ | async"></my-transaction-form>

transaction.component.ts

export class TransactionFormComponent implements OnInit {
	pageTransaction$: BehaviorSubject<ITransaction> = new BehaviorSubject<ITransaction>(null);
	ngOnInit(): void {
		this._route.params
			.switchMap(params => {
				return this._transactionService.GetTransaction(params['id']);
			})
			.subscribe(data => {
				// data successfully returned a transaction
				this.pageTransaction$.next(data);
			},
			error => {
				// if undefined parameter, create new instance
				this.pageTransaction$.next(Transaction.NewTransaction(1));
			});
		}
}