@Nullable
    @Override
    public Boolean isResponseStreaming(Type returnType, @Nullable MediaType produceType) {
        final Class<?> clazz = typeToClass(unwrapUnaryAsyncType(returnType));
        if (clazz == null) {
            return null;
        }

        if (HttpFile.class.isAssignableFrom(clazz)) {
            return true;
        }
        return null;
    }
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