@Override
    public AbstractHttpMessageBuilder trailers(
            Iterable<? extends Entry<? extends CharSequence, String>> trailers) {
        requireNonNull(trailers, "trailers");
        if (httpTrailers == null) {
            httpTrailers = HttpHeaders.builder();
        }
        httpTrailers.add(trailers);
        return this;
    }
Returns the {@link Publisher} that was set by {@link #content(MediaType, Publisher)}.
core/src/main/java/com/linecorp/armeria/common/AbstractHttpMessageBuilder.java