reactor-core/src/main/java/reactor/core/Exceptions.java
public static RejectedExecutionException failWithRejected(Throwable cause) {
		if (cause instanceof ReactorRejectedExecutionException) {
			return (RejectedExecutionException) cause;
		}
		return new ReactorRejectedExecutionException("Scheduler unavailable", cause);
	}
public static RejectedExecutionException failWithRejected(Throwable cause) {
		if (cause instanceof ReactorRejectedExecutionException) {
			return (RejectedExecutionException) cause;
		}
		return new ReactorRejectedExecutionException("Scheduler unavailable", cause);
	}
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