How to dispatch an empty action?

I am using ngrx/effects.

How can I dispatch an empty action?

This is how I am doing now:

 @Effect() foo$ = this.actions$
    .ofType(Actions.FOO)
    .withLatestFrom(this.store, (action, state) => ({ action, state }))
    .map(({ action, state }) => {
      if (state.foo.isCool) {
        return { type: Actions.BAR };
      } else {
        return { type: 'NOT_EXIST' };
      }
    });

Since I have to return an action, I am using return { type: 'NOT_EXIST' };.

Is there a better way to do this?

I've used similar unknown actions, but usually in the context of unit tests for reducers.

If you are uneasy about doing the same in an effect, you could conditionally emit an action using mergeMap, Observable.of() and Observable.empty() instead:

@Effect() foo$ = this.actions$
  .ofType(ChatActions.FOO)
  .withLatestFrom(this.store, (action, state) => ({ action, state }))
  .mergeMap(({ action, state }) => {
    if (state.foo.isCool) {
      return Observable.of({ type: Actions.BAR });
    } else {
      return Observable.empty();
    }
  });