public HttpService orElse(HttpService nextService) {
        requireNonNull(nextService, "nextService");
        return new OrElseHttpService(this, nextService);
    }
Creates a new {@link HttpService} that tries this {@link FileService} first and then the specified
{@link HttpService} when this {@link FileService} does not have a requested resource.

@param nextService the {@link HttpService} to try secondly
core/src/main/java/com/linecorp/armeria/server/file/FileService.java