Fix NPE in ServerGrpcChannelBackoffResetHandler

[timothy-e]

Pinot integration tests failed flakily with

java.lang.NullPointerException
	at org.apache.pinot.server.starter.helix.ServerGrpcChannelBackoffResetHandler.onInstanceConfigChange(ServerGrpcChannelBackoffResetHandler.java:90)
	at org.apache.helix.manager.zk.CallbackHandler.invoke(CallbackHandler.java:362)
	at org.apache.helix.manager.zk.CallbackHandler.reset(CallbackHandler.java:772)
	at org.apache.helix.manager.zk.ZKHelixManager.resetHandlers(ZKHelixManager.java:1195)
	at org.apache.helix.manager.zk.ZKHelixManager$1.run(ZKHelixManager.java:931)

getPathChanged can return null when the notification type is FINALIZE. This was originally present in the PR that introduced this file, but removed because it was accidentally viewed as redundant.

Also, add a defensive null check before using the pathChanged, since it isn't guaranteed that pathChanged will be non-null.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 63.11%. Comparing base (52554ab) to head (32468ce).
⚠️ Report is 12 commits behind head on master.

Files with missing lines	Patch %	Lines
...er/helix/ServerGrpcChannelBackoffResetHandler.java	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #18139      +/-   ##
============================================
- Coverage     64.01%   63.11%   -0.90%     
  Complexity     1617     1617              
============================================
  Files          3192     3202      +10     
  Lines        193936   194724     +788     
  Branches      29937    30049     +112     
============================================
- Hits         124140   122900    -1240     
- Misses        59990    62078    +2088     
+ Partials       9806     9746      -60     

Flag	Coverage Δ
custom-integration1	100.00% <ø> (ø)
integration	100.00% <ø> (ø)
integration1	100.00% <ø> (ø)
integration2	0.00% <ø> (ø)
java-11	63.06% <66.66%> (-0.89%)	⬇️
java-21	63.04% <66.66%> (-0.95%)	⬇️
temurin	63.11% <66.66%> (-0.90%)	⬇️
unittests	63.11% <66.66%> (-0.90%)	⬇️
unittests1	55.55% <ø> (-0.32%)	⬇️
unittests2	33.52% <66.66%> (-0.87%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[Jackie-Jiang]

We should dig deeper. Do you see a code path in Helix that can result in null pathChanges?