reactor-core/src/main/java/reactor/core/Exceptions.java
public static RuntimeException propagate(Throwable t) {
		throwIfFatal(t);
		if (t instanceof RuntimeException) {
			return (RuntimeException) t;
		}
		return new ReactiveException(t);
	}
public static RuntimeException propagate(Throwable t) {
		throwIfFatal(t);
		if (t instanceof RuntimeException) {
			return (RuntimeException) t;
		}
		return new ReactiveException(t);
	}
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.