message: docs: changes for typescript 2.7
  Because of changes in Typescript a property must have an initializer
  or be set to undefined.
  PR Close
diff: @@ -19,7 +19,7 @@ export class HeroesComponent implements OnInit {
  heroes = HEROES;
  // #enddocregion component
  // #docregion on-select
  - selectedHero: Hero;
  + selectedHero?: Hero;
  // #enddocregion on-select
  constructor() { }
  @@ -35,4 +35,3 @@ export class HeroesComponent implements OnInit {
  // #docregion component
  }
  // #enddocregion component
  -
  