Fix NPE in IntermedaiteStateCalcStage

[GrantPSpencer]

Issues

• My PR addresses the following Helix issues and references them in the PR description:

#2973

Description

• Here are some details about my PR, including screenshots of any UI changes:

NPE can occur during IntermedaiteStateCalcStage
Details can be found in the issue page #2973

Tests

• The following tests are written for this issue:

testMessageAlreadyApplied in TestIntermediateStateCalcStage
Without the null check in in IntermediateStateCalcStage, this will produce an identical NPE

• The following is the result of the "mvn test" command on the appropriate module:

$ mvn test -o -Dtest=TestIntermediateStateCalcStage -pl=helix-core

[INFO] Tests run: 5, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 14.973 s - in org.apache.helix.controller.stages.TestIntermediateStateCalcStage
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  53.225 s
[INFO] Finished at: 2024-11-27T11:03:45-08:00
[INFO] ------------------------------------------------------------------------

Changes that Break Backward Compatibility (Optional)

• My PR contains changes that break backward compatibility or previous assumptions for certain methods or API. They include:
  N/A

Documentation (Optional)

• In case of new functionality, my PR adds documentation in the following wiki page:

(Link the GitHub wiki you added)

Commits

• My commits all reference appropriate Apache Helix GitHub issues in their subject lines. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Code Quality

• My diff has been formatted using helix-style.xml
  (helix-style-intellij.xml if IntelliJ IDE is used)

[xyuanlu]

Thanks for fixing the test!! Good job!

[junkaixue]

why not use else if instead of inner if statement.

[GrantPSpencer]

Good catch. Was just coding on auto pilot. Updated

[GrantPSpencer]

Pull request approved by: @junkaixue
Commit message: Fix NPE in IntermediateStateCalcStage

CI Failed due to recurrent flaky test simpleMasterSlaveTest
#2927