@Override
                protected void beforeComplete(Subscriber<? super HttpObject> subscriber) {
                    if (!trailers.isEmpty() && !trailerSent) {
                        subscriber.onNext(trailers);
                    }
                }
A response converter implementation which creates an {@link HttpResponse} when the {@code result} is
an instance of {@link HttpFile}.
core/src/main/java/com/linecorp/armeria/server/annotation/HttpFileResponseConverterFunction.java