[ISSUES #8635] fix a NPE when call the shutdown method

[onewe]

Close #8635

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[codecov-commenter]

Codecov Report

Merging #8636 (46164cb) into develop (f3d134d) will decrease coverage by 0.01%.
The diff coverage is 66.66%.

@@              Coverage Diff              @@
##             develop    #8636      +/-   ##
=============================================
- Coverage      41.58%   41.57%   -0.02%     
+ Complexity      4459     4458       -1     
=============================================
  Files            882      882              
  Lines          32124    32127       +3     
  Branches        3719     3721       +2     
=============================================
- Hits           13359    13357       -2     
- Misses         17416    17417       +1     
- Partials        1349     1353       +4     

Impacted Files	Coverage Δ
...s/naming/consistency/persistent/raft/RaftCore.java	9.88% <66.66%> (-0.04%)	⬇️
.../naming/push/v1/NamingSubscriberServiceV1Impl.java	66.66% <0.00%> (-15.88%)	⬇️
...m/alibaba/nacos/naming/misc/HttpClientManager.java	69.04% <0.00%> (-14.29%)	⬇️
...ent/manager/impl/EphemeralIpPortClientManager.java	68.00% <0.00%> (-2.00%)	⬇️
...alibaba/nacos/core/remote/control/TpsRecorder.java	74.32% <0.00%> (-1.36%)	⬇️
...va/com/alibaba/nacos/naming/utils/ServiceUtil.java	50.40% <0.00%> (-0.81%)	⬇️
...a/com/alibaba/nacos/naming/push/v1/PushClient.java	46.93% <0.00%> (ø)
...te/rpc/handler/SubscribeServiceRequestHandler.java	100.00% <0.00%> (ø)
.../core/v2/event/publisher/NamingEventPublisher.java	76.25% <0.00%> (+1.25%)	⬆️
.../com/alibaba/nacos/common/notify/NotifyCenter.java	53.84% <0.00%> (+7.69%)	⬆️
... and 1 more

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