[Repository Plugin] Fix stats test

[gbbafna]

Description

Using null as default for extended stats. This helps in identifying whether the blobstore supports extended stats or not . The current presence of empty map doesn't help to differentiate whether the blobstore supports extended stats or if there are no requests at all .

In #10735 , one node was having requests , hence was populating extended stats , whereas the other node was having no request , it was populating stats. This caused issues while merging repository stats across the nodes.

Related Issues

Resolves #[10735]

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Failing checks are inspected and point to the corresponding known issue(s) (See: Troubleshooting Failing Builds)
• Commits are signed per the DCO using --signoff
• Commit changes are listed out in CHANGELOG.md file (See: Changelog)
• Public documentation issue/PR created

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[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/28896/
• CommitID: 000b16f
  Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green.
  Is the failure a flaky test unrelated to your change?

[github-actions]

Compatibility status:

Checks if related components are compatible with change 000b16f

Incompatible components

Incompatible components: [https://github.com/opensearch-project/cross-cluster-replication.git]

Skipped components

Compatible components

Compatible components: [https://github.com/opensearch-project/security.git, https://github.com/opensearch-project/alerting.git, https://github.com/opensearch-project/index-management.git, https://github.com/opensearch-project/anomaly-detection.git, https://github.com/opensearch-project/job-scheduler.git, https://github.com/opensearch-project/sql.git, https://github.com/opensearch-project/asynchronous-search.git, https://github.com/opensearch-project/common-utils.git, https://github.com/opensearch-project/observability.git, https://github.com/opensearch-project/k-nn.git, https://github.com/opensearch-project/reporting.git, https://github.com/opensearch-project/security-analytics.git, https://github.com/opensearch-project/custom-codecs.git, https://github.com/opensearch-project/performance-analyzer.git, https://github.com/opensearch-project/opensearch-oci-object-storage.git, https://github.com/opensearch-project/ml-commons.git, https://github.com/opensearch-project/performance-analyzer-rca.git, https://github.com/opensearch-project/geospatial.git, https://github.com/opensearch-project/notifications.git, https://github.com/opensearch-project/neural-search.git]

[opensearch-trigger-bot]

This PR is stalled because it has been open for 30 days with no activity.

[kotwanikunal]

The PR has been stalled for quite a while. Please reopen if you are still working on it.