message: docs: fix issue
  setting the `hero` property as an optional property fixes the compilation
  error: `Property 'hero' has no initializer and is not definitely assigned
  in the constructor` when having the ts transpiler set to "strict" mode.
  PR Close
diff: @@ -13,7 +13,7 @@ import { Hero } from '../hero';
  })
  export class HeroDetailComponent implements OnInit {
  // #docregion input-hero
  - @Input() hero: Hero;
  + @Input() hero?: Hero;
  // #enddocregion input-hero
  constructor() { }
  