Wrap source emission only if its not empty

index.js

const { rxObserver } = require('api/v0.3');
const { timer, of, Notification, EMPTY, merge, concat, throwError } = require('rxjs');
const { switchMap, materialize, dematerialize, delay, map } = require('rxjs/operators');

const source$ = merge(timer(5), timer(10));

// Uncomment next line to get an empty source
// const source$ = EMPTY;

// Uncomment next line to get a source with an error
// const source$ = concat(timer(5), throwError('Err'));

const result$ = source$.pipe(
  // turn all events on stream into Notifications
  materialize(),

  // wrap elements only if they are present
  switchMap((event, index) => {
    // if its first event and its a value
    if (index === 0 && event.kind === 'N') {
      const startingNotification = new Notification('N', '>>>', undefined);
      return of(startingNotification, event);
    }

    // if its a completion event and it not a first event
    if (index > 0 && event.kind === 'C') {
      const endingNotification = new Notification('N', '<<<', undefined);
      return of(endingNotification, event);
    }

    return of(event);
  }),

  // turn Notifications back to events on stream
  dematerialize()
);

source$.subscribe(rxObserver('source$'));
result$.subscribe(rxObserver('result$'));