[ML] Omit uncomputed model stats

[prwhelan]

There is a chance that a model does not have its stats computed when usage is called, potentially throwing a NullPointerException. Usage will now skip models that do not have stats yet.

[elasticsearchmachine]

Pinging @elastic/ml-core (Team:ML)

[elasticsearchmachine]

Hi @prwhelan, I've created a changelog YAML for you.

[github-actions]

🔍 Preview links for changed docs

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[github-actions]

ℹ️ Important: Docs version tagging

👋 Thanks for updating the docs! Just a friendly reminder that our docs are now cumulative. This means all 9.x versions are documented on the same page and published off of the main branch, instead of creating separate pages for each minor version.

We use applies_to tags to mark version-specific features and changes.

Expand for a quick overview

When to use applies_to tags:

✅ At the page level to indicate which products/deployments the content applies to (mandatory)
✅ When features change state (e.g. preview, ga) in a specific version
✅ When availability differs across deployments and environments

What NOT to do:

❌ Don't remove or replace information that applies to an older version
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❌ Don't forget that applies_to tags can be used at the page, section, and inline level

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• Check out the cumulative docs guidelines
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[Copilot]

Pull request overview

Fixes ML usage reporting to avoid a potential NullPointerException when trained model size stats have not yet been computed, by omitting those uncomputed stats from the aggregated usage output.

Changes:

• Add a null-check around modelSizeStats when aggregating trained model memory usage in ML usage reporting.
• Add a unit test covering the case where modelSizeStats is null.
• Add a changelog entry for the bug fix.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/MachineLearningUsageTransportAction.java	Avoids NPE by skipping memory aggregation when modelSizeStats is missing.
x-pack/plugin/ml/src/test/java/org/elasticsearch/xpack/ml/MachineLearningUsageTransportActionTests.java	Adds regression test for null modelSizeStats.
docs/changelog/146186.yaml	Documents the bug fix in the changelog.

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[edsavage]

LGTM

[elasticsearchmachine]

💚 Backport successful

Status	Branch	Result
✅	9.2
✅	8.19
✅	9.3
✅	9.4