p.location-badge.
  exported from <a href='../di'>angular2/di</a>
  defined in <a href="https://github.com/angular/angular/tree/master/modules/angular2/src/di/annotations_impl.ts#L54-L72">angular2/src/di/annotations_impl.ts (line 54)</a>

:markdown
  A parameter annotation that marks a dependency as optional. <a href='Injector-class.html'><code>Injector</code></a> provides `null` if
  the dependency is not found.
  
  ```
  class AComponent {
    constructor(@Optional() aService:MyService) {
      this.aService = aService;
    }
  }
  ```