code: public static RuntimeException propagate(Throwable t) {
  		throwIfFatal(t);
  		if (t instanceof RuntimeException) {
  			return (RuntimeException) t;
  		}
  		return new ReactiveException(t);
  	}
docs: Prepare an unchecked {@link RuntimeException} that should be propagated
  downstream through {@link org.reactivestreams.Subscriber#onError(Throwable)}.
  <p>This method invokes {@link #throwIfFatal(Throwable)}.
  
  @param t the root cause
  
  @return an unchecked exception to propagate through onError signals.