code: public final Flux<T> doOnTerminate(Runnable onTerminate) {
  		Objects.requireNonNull(onTerminate, "onTerminate");
  		return doOnSignal(this,
  				null,
  				null,
  				e -> onTerminate.run(),
  				onTerminate,
  				null,
  				null,
  				null);
  	}
docs: Add behavior (side-effect) triggered when the {@link Flux} terminates, either by
  completing successfully or with an error.
  <p>
  <img class="marble" src="doc-files/marbles/doOnTerminateForFlux.svg" alt="">
  
  @param onTerminate the callback to call on {@link Subscriber#onComplete} or {@link Subscriber#onError}
  
  @return an observed  {@link Flux}