private Pair<Boolean, SelectorData> matchSelector(final ServerWebExchange exchange, final Collection<SelectorData> selectors) {
        List<SelectorData> filterCollectors = selectors.stream()
                .filter(selector -> selector.getEnabled() && filterSelector(selector, exchange))
                .distinct()
                .collect(Collectors.toList());
        if (filterCollectors.size() > 1) {
            return Pair.of(Boolean.FALSE, manyMatchSelector(filterCollectors));
        } else {
            return Pair.of(Boolean.TRUE, filterCollectors.stream().findFirst().orElse(null));
        }
    }
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