reactor-core/src/main/java/reactor/core/publisher/Operators.java
public static void error(Subscriber<?> s, Throwable e) {
		s.onSubscribe(EmptySubscription.INSTANCE);
		s.onError(e);
	}
public static void error(Subscriber<?> s, Throwable e) {
		s.onSubscribe(EmptySubscription.INSTANCE);
		s.onError(e);
	}
Calls onSubscribe on the target Subscriber with the empty instance followed by a call to onError with the
supplied error.

@param s target Subscriber to error
@param e the actual error