@Override
        public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
            if (!(evt instanceof UpgradeEvent)) {
                ctx.fireUserEventTriggered(evt);
                return;
            }

            final UpgradeEvent upgradeEvt = (UpgradeEvent) evt;
            if (upgradeEvt == UpgradeEvent.UPGRADE_ISSUED) {
                // Uninterested in this event
                return;
            }

            this.upgradeEvt = upgradeEvt;
        }
Keeps the upgrade result in {@link #upgradeEvt}.
core/src/main/java/com/linecorp/armeria/client/HttpClientPipelineConfigurator.java