code: public final Disposable subscribe(@Nullable Consumer<? super T> onNext, Consumer<? super Throwable>
  			onError){
  		return subscribe(onNext, onError, null);
  	}
docs: Subscribes to this {@link ParallelFlux} by providing an onNext and onError callback
  and triggers the execution chain for all 'rails'.
  
  @param onNext consumer of onNext signals
  @param onError consumer of error signal