@UnstableApi
    public FutureTransformingRequestPreparation<T> recover(
            Function<? super Throwable, ? extends @Nullable T> function) {
        requireNonNull(function, "function");
        errorHandler(function);
        return this;
    }
Recovers a failed {@link HttpResponse} by switching to a returned fallback object returned by the
{@code function}. If a {@code null} value is returned, the cause will not be recovered.
core/src/main/java/com/linecorp/armeria/client/FutureTransformingRequestPreparation.java