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