see more from https://github.com/openzipkin/brave/issues/867, also see https://github.com/apache/incubator-dubbo/issues/3576
attachments.put(key, value);
        }
        return this;
    }
    /**
     * remove attachment.
     *
     * @param key
     * @return context
     */
    public RpcContext removeAttachment(String key) {
        attachments.remove(key);
        return this;
    }
    /**
     * get attachments.
     *
     * @return attachments
     */
    public Map<String, String> getAttachments() {
        return attachments;
    }
    /**
     * set attachments
     *
     * @param attachment
     * @return context
     */
    public RpcContext setAttachments(Map<String, String> attachment) {
        this.attachments.clear();