Rollbar instantiation returns null in Angular 2

Question

I am trying to integrate Rollbar in Angular2 and following the example they have on their website.

But when I run npm start it gives me the following error

here is the code in app.module.ts

    const rollbarConfig = {
        accessToken: 'ACCESS_TOKEN',
        captureUncaught: true,
        captureUnhandledRejections: true,
    };

    export function getRollbarConfig() {
        return () => new Rollbar(rollbarConfig);
    }
    @Injectable()
    export class RollbarErrorHandler implements ErrorHandler {
        constructor(private injector: Injector) { }
        handleError(err:any) : void {
            var rollbar = this.injector.get(Rollbar);
            rollbar.error(err.originalError || err);
        }
    }
    .
    .
    .
    @NgModule({
        providers: [
            .
            .
            .
            { provide: Http, useClass: AuthenticatedHttpService },
            BaseRequestOptions,
            CronBuilderService,
            { provide: ErrorHandler, useClass: RollbarErrorHandler },
            { provide: Rollbar, useFactory: getRollbarConfig },
        ],
        .
        .
        .
    })

If I remove this line provide: Rollbar, useFactory: getRollbarConfig it works and successfully compiled. Thanks.