private Boolean filterSelector(final SelectorData selector, final ServerWebExchange exchange) {
        if (selector.getType() == SelectorTypeEnum.CUSTOM_FLOW.getCode()) {
            if (CollectionUtils.isEmpty(selector.getConditionList())) {
                return false;
            }
            return MatchStrategyFactory.match(selector.getMatchMode(), selector.getConditionList(), exchange);
        }
        return true;
    }
Handle rule if null mono.

@param pluginName the plugin name
@param exchange the exchange
@param chain the chain
@return the mono
shenyu-plugin/shenyu-plugin-base/src/main/java/org/apache/shenyu/plugin/base/AbstractShenyuPlugin.java