@Override
    public AbstractHttpMessageBuilder trailer(CharSequence name, Object value) {
        requireNonNull(name, "name");
        requireNonNull(value, "value");
        if (httpTrailers == null) {
            httpTrailers = HttpHeaders.builder();
        }
        httpTrailers.addObject(name, value);
        return this;
    }
Returns the {@link Publisher} that was set by {@link #content(MediaType, Publisher)}.
core/src/main/java/com/linecorp/armeria/common/AbstractHttpMessageBuilder.java