Fix NPE in bitmap terms lookup when stored field is missing

[kshitizj03]

Description

A terms query using terms lookup with value_type: bitmap and store: true throws a
NullPointerException when the looked-up document exists but the stored field at path is
missing.

Root cause: in TermsQueryBuilder#fetch, getResponse.getField(termsLookup.path()) returns
null for an absent stored field, and getValues() was called on it unconditionally.

This change guards the null DocumentField and treats a missing stored field as no terms
(no matches), which is consistent with how a missing source field is already handled. Existing
single-value bitmap validation is preserved for the present-field case.

Added a REST yaml test in search/380_bitmap_filtering.yml: a lookup document missing the stored
bitmap field now returns hits.total: 0 instead of erroring.

Related Issues

Resolves #21995

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

[github-actions]

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🧪 PR contains tests

🔒 No security concerns identified

✅ No TODO sections

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⚡ No major issues detected

[github-actions]

PR Code Suggestions ✨

Explore these optional code suggestions:

Category	Suggestion	Impact
Possible issue	Add null check for values list Add a null check for storedField.getValues() before accessing it. Even when storedField is not null, getValues() could potentially return null, which would cause a NullPointerException when calling size(). server/src/main/java/org/opensearch/index/query/TermsQueryBuilder.java [586-597] DocumentField storedField = getResponse.getField(termsLookup.path()); // A stored field that is absent from the looked-up document yields a null // DocumentField; treat it as no terms (no matches) instead of failing. if (storedField != null) { List<Object> values = storedField.getValues(); - if (values.size() != 1 && valueType == ValueType.BITMAP) { - throw new IllegalArgumentException( - "Invalid value for bitmap type: Expected a single base64 encoded serialized bitmap." - ); + if (values != null) { + if (values.size() != 1 && valueType == ValueType.BITMAP) { + throw new IllegalArgumentException( + "Invalid value for bitmap type: Expected a single base64 encoded serialized bitmap." + ); + } + terms.addAll(values); } - terms.addAll(values); } Suggestion importance[1-10]: 3 __ Why: While adding a null check for values is defensive programming, the DocumentField.getValues() method typically returns an empty list rather than null. The suggestion addresses a theoretical edge case but may not reflect actual API behavior, making it a minor improvement at best.	Low

[github-actions]

❌ Gradle check result for 3b8d5e2: FAILURE

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?

[kshitizj03]

The gradle-check failure looks like an unrelated CI flake rather than a real test failure.

The failing task is :plugins:analysis-phonetic:test, and the cause is a Gradle worker connection problem, not a test assertion:

org.gradle.internal.remote.internal.ConnectException: Could not connect to server [...127.0.0.1...]. Connection refused
MessageIOException: Could not read message from '/127.0.0.1:49564'

The Jenkins run also reports "Test Result (no failures)", and :server:test passed in the same run. This change only touches bitmap terms lookup in :server, and the bitmap REST suite (search/380_bitmap_filtering, including the new missing-field case) passes locally.

Could a maintainer please re-run gradle-check? Thanks!