Revert "remove unnecessary optional property"

[mshima]

Reverts #19427 once angular/angular#46918 has been resolved.

Related to #19373

[ertunga]

@mshima I think we can merge this without waiting. Mentioned lines in the issue are wrapped with ngIf checks that make sure the fields are there. Even the fields can be null or undefined, because of the ngIf ?. can be removed here.

Here is an example, we can remove the question mark here.

<div *ngIf="post.blog"> <a [routerLink]="['/blog', post.blog.id, 'view']">{{ post.blog?.name }}</a> </div>