code: public static RejectedExecutionException failWithRejected(Throwable cause) {
  		if (cause instanceof ReactorRejectedExecutionException) {
  			return (RejectedExecutionException) cause;
  		}
  		return new ReactorRejectedExecutionException("Scheduler unavailable", cause);
  	}
docs: Return a new {@link RejectedExecutionException} with standard message and cause,
  unless the {@code cause} is already a {@link RejectedExecutionException} created
  via {@link #failWithRejected(Throwable)} (not the singleton-producing variants).
  
  @param cause the original exception that caused the rejection
  @return a new {@link RejectedExecutionException} with standard message and cause