@Bean
    public MetaDataSubscriber commonMetaDataSubscriber(final ObjectProvider<List<MetaDataHandler>> metaDataHandlerList) {
        return new CommonMetaDataSubscriber(metaDataHandlerList.getIfAvailable(Collections::emptyList));
    }
common meta data subscriber.

@param metaDataHandlerList the meta data handler list
@return the meta data subscriber
shenyu-spring-boot-starter/shenyu-spring-boot-starter-gateway/src/main/java/org/apache/shenyu/springboot/starter/gateway/ShenyuConfiguration.java