Inject service into gateway - NestJS

Question

Am completely new to nestjs and trying to inject a service into a gateway. Not able to get it to work. Following is the code,

#notification.gateway.ts

@WebSocketGateway()
export  class  NotificationsGateway implements  OnGatewayConnection {
    constructor(private  notificationService: NotificationsService) {}
    
    afterInit(server: any) {
        this.notificationService.server = server;
    }
}

#notification.service.ts

@Injectable()
export  class  NotificationsService {
    public  server: Server = null;
        
    // Removing the inject model line makes the service available in the gateway
    constructor(
        @InjectModel(Notification.name) 
        private  notificationModel: Model<NotificationDocument>
    ) {}
}

#notifications.module.ts

import { TenancyModule } from '../tenancy';

@Module({
  imports: [
    TenancyModule.forFeature([
      { name: Notification.name, schema: NotificationSchema },
    ]),
  ],
  providers: [NotificationsService, NotificationsGateway]
})
export class NotificationsModule {}

Am getting the following error,

TypeError: Cannot set property 'server' of undefined
    at NotificationsGateway.afterInit (c:\notifications\notifications.gateway.js:25:41)

Removing the InjectModel in the service constructor makes the service available, but I would the model to persist the notifications.

Any help on how to resolve this highly appreciated. Thanks.