code: public final <E extends Throwable> Mono<T> doOnError(Class<E> exceptionType,
  			final Consumer<? super E> onError) {
  		Objects.requireNonNull(exceptionType, "type");
  		@SuppressWarnings("unchecked")
  		Consumer<Throwable> handler = (Consumer<Throwable>)onError;
  		return doOnError(exceptionType::isInstance, handler);
  	}
docs: Add behavior triggered when the {@link Mono} completes with an error matching the given exception type.
  <p>
  <img class="marble" src="doc-files/marbles/doOnErrorWithClassPredicateForMono.svg" alt="">
  
  @param exceptionType the type of exceptions to handle
  @param onError the error handler for relevant errors
  @param <E> type of the error to handle
  
  @return an observed  {@link Mono}