private static ServerSentEvent toSse(@Nullable Object content) {
        if (content == null) {
            return ServerSentEvent.empty();
        }
        if (content instanceof ServerSentEvent) {
            return (ServerSentEvent) content;
        }
        return ServerSentEvent.ofData(String.valueOf(content));
    }
A response converter implementation which creates an {@link HttpResponse} with
{@code content-type: text/event-stream}. The objects published from a {@link Publisher} or {@link Stream}
would be converted into Server-Sent Events if a {@link ProducesEventStream} annotation is specified
on an annotated service method.
core/src/main/java/com/linecorp/armeria/server/annotation/ServerSentEventResponseConverterFunction.java