@Bean
    @ConditionalOnMissingBean(FallbackHandler.class)
    public FallbackHandler fallbackHandler() {
        return new SentinelFallbackHandler();
    }
Fallback handler.

@return the default fallback handler
shenyu-spring-boot-starter/shenyu-spring-boot-starter-plugin/shenyu-spring-boot-starter-plugin-sentinel/src/main/java/org/apache/shenyu/springboot/starter/plugin/sentinel/SentinelPluginConfiguration.java