What does null mean! in TypeScript?

I have seen null !

many times in Angular source code. What does the following sign mean !

?

:

• https://github.com/angular/angular/blob/master/packages/router/src/router.ts#L221

  private navigations = new BehaviorSubject<NavigationParams>(null !);
  
        
  
          
          
          
        
  
      

• https://github.com/angular/angular/blob/master/packages/router/src/router.ts#L357

  this.locationSubscription = null !;