Issue Description

Type: bug report

Describe what happened

Describe what you expected to happen

How to reproduce it (as minimally and precisely as possible)

1. springcloud-gateway 3.1.4版本使用sentinel 1.8.6版本运行时会报空指针异常
2. sentinel相关依赖如下所示： com.alibaba.cloud spring-cloud-starter-alibaba-sentinel com.alibaba.csp sentinel-datasource-nacos 1.8.6 com.alibaba.cloud spring-cloud-alibaba-sentinel-gateway
3. 异常如下所示：
   java.lang.NullPointerException: value
   at java.base/java.util.Objects.requireNonNull(Objects.java:246) ~[na:na]
   at reactor.util.context.Context2.put(Context2.java:46) ~[reactor-core-3.4.24.jar:3.4.24]
   at com.alibaba.csp.sentinel.adapter.reactor.SentinelReactorSubscriber.currentContext(SentinelReactorSubscriber.java:70) ~[sentinel-reactor-adapter-1.8.6.jar:na]
   at com.alibaba.csp.sentinel.adapter.reactor.SentinelReactorSubscriber.currentContext(SentinelReactorSubscriber.java:69) ~[sentinel-reactor-adapter-1.8.6.jar:na]
   at reactor.core.publisher.FluxPeek$PeekSubscriber.currentContext(FluxPeek.java:120) ~[reactor-core-3.4.24.jar:3.4.24]
   at reactor.core.publisher.InnerOperator.currentContext(InnerOperator.java:33) ~[reactor-core-3.4.24.jar:3.4.24]
   at reactor.core.publisher.InnerOperator.currentContext(InnerOperator.java:33) ~[reactor-core-3.4.24.jar:3.4.24]
   at reactor.core.publisher.InnerOperator.currentContext(InnerOperator.java:33) ~[reactor-core-3.4.24.jar:3.4.24]