reactor-core/src/main/java/reactor/core/publisher/Mono.java
public final Mono<T> onErrorReturn(Predicate<? super Throwable> predicate, T fallbackValue) {
		return onErrorResume(predicate,  throwable -> just(fallbackValue));
	}
public final Mono<T> onErrorReturn(Predicate<? super Throwable> predicate, T fallbackValue) {
		return onErrorResume(predicate,  throwable -> just(fallbackValue));
	}
Simply emit a captured fallback value when an error matching the given predicate is
observed on this {@link Mono}.
<p>
<img class="marble" src="doc-files/marbles/onErrorReturnForMono.svg" alt="">

@param predicate the error predicate to match
@param fallbackValue the value to emit if an error occurs that matches the predicate

@return a new {@link Mono}