Fix unexpected error when following the tutorial (when going through it with stricter type checking enforced). While (+) converts a string to an integer, it does not account for the possibility that `this.route.snapshot.paramMap.get('id')` could return null (type: string | null). Since this null case is not a practical outcome, it is a matter of types; switching from (+) to the `Number` function eliminates this issue, making the tutorial more robust.
PR Close#41570
5e8dcfd641