@SentinelRestTemplate fallback doesn't work and NullPointerException throws

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Which Component
Sentinel
Describe the bug
The RestTempte configuration:

@Bean
@LoadBalanced
@SentinelRestTemplate(blockHandler = "handleBlock", blockHandlerClass = RestTemplateBlock::class, fallback = "handleFallback", fallbackClass = RestTemplateFallback::class)
open fun restTemplate(clientHttpRequestFactory: ClientHttpRequestFactory): RestTemplate {
	val restTemplate = RestTemplate(clientHttpRequestFactory)
	restTemplate.messageConverters.add(MappingJackson2HttpMessageConverterImpl())
	return restTemplate
}

fallbackClass Configuration:

class RestTemplateFallback {
    companion object {
        @JvmStatic
        fun handleFallback(request: HttpRequest, body: ByteArray, execution: ClientHttpRequestExecution, exception: BlockException): ClientHttpResponse {
            println(">>> RestTemplateFallback.handleFallback")
            return SentinelClientHttpResponse()
        }
    }
}

The service service-res doesn't exist or already offline .

 val resp = restTemplate.getForEntity("http://service-res/res/api/ms/app", Result::class.java)

The NullPointerException occured:

java.lang.NullPointerException: null
	at org.springframework.web.client.DefaultResponseErrorHandler.hasError(DefaultResponseErrorHandler.java:64) ~[spring-web-5.3.5.jar:5.3.5]
	at org.springframework.web.client.RestTemplate.handleResponse(RestTemplate.java:807) ~[spring-web-5.3.5.jar:5.3.5]
	at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:777) ~[spring-web-5.3.5.jar:5.3.5]
	at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:711) ~[spring-web-5.3.5.jar:5.3.5]
	at org.springframework.web.client.RestTemplate.getForEntity(RestTemplate.java:361) ~[spring-web-5.3.5.jar:5.3.5]

I trace the class SentinelProtectInterceptor.intercept
found that the exception has be catched and the IllegalStateException is not BlockException, so it do nothing.
java.lang.IllegalStateException: No instances available for service-res

I think that sentinel with openfeign work fine, why RestTemplate not,and I saw the SentinelInvocationHandler's process:

I am confused !!!

I configed the SentinelRestTemplate fallbackClass, if can't access the service ,it shouldn't run the method handleFallback?

<org.springframework.boot.version>2.4.4</org.springframework.boot.version>
<org.springframework.data.version>2.4.4</org.springframework.data.version>
<org.springframework.cloud.version>2020.0.2</org.springframework.cloud.version>
<com.alibaba.cloud.version>2021.1</com.alibaba.cloud.version>

[ankeway]

See
#1346
4c5bf77

[theonefx]

My solution is to simply throw the exception when it can't be handled.

#2146