IServiceEndpointNotificationService is returning null all the time.

Below is my code snippet. However, I got null everytime from the service. Any idea how can I resolve it?

IServiceEndpointNotificationService cloudService = (IServiceEndpointNotificationService)serviceProvider.GetService(typeof(IServiceEndpointNotificationService));
            if (cloudService == null)
                throw new InvalidPluginExecutionException("Failed to retrieve the service bus service.");