fix: handle Document with content=None in DocumentLanguageClassifier

[rautaditya2606]

Related Issues

• fixes bug: DocumentLanguageClassifier crashes with TypeError when Document has content=None #11418

Proposed Changes

• Guard Document entries with content=None in DocumentLanguageClassifier._detect_language() to log a warning and return unmatched instead of crashing.
• Added regression test for the None content case.
• Added release note.

How did you test it?

• hatch run test:unit test/components/classifiers/test_document_language_classifier.py -k none_content

Notes for the reviewer

• Keeps behavior consistent with existing unmatched handling when LangDetectException is raised.
• Document.content is explicitly allowed to be None (blob-only documents), so this is a valid edge case the classifier should handle gracefully.

Checklist

• I have read the contributors guidelines and the code of conduct.
• I have updated the related issue with new insights and changes.
• I have added unit tests and updated the docstrings.
• I've used one of the conventional commit types for my PR title.
• I have documented my code.
• I have added a release note file, following the contributors guidelines.
• I have run pre-commit hooks and fixed any issue.

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Pull request overview

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This PR prevents DocumentLanguageClassifier from crashing when a Document has content=None, treating it as “unmatched” and logging a warning.

Changes:

• Add an early-return in language detection when Document.content is None (with a warning log).
• Add a regression test to ensure None content is marked as unmatched and emits a warning.
• Add release notes describing the fix.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
test/components/classifiers/test_document_language_classifier.py	Adds a regression test for content=None behavior.
haystack/components/classifiers/document_language_classifier.py	Handles Document.content is None without crashing and logs a warning.
releasenotes/notes/document-language-classifier-none-content-a245d044b02a19b0.yaml	Documents the fix in the release notes.

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Project	Deployment	Actions	Updated (UTC)
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[julian-risch]

Looks good to me! Thank you for your contribution @rautaditya2606 !
I made two small edits. I thought about another edit to address that we are now emitting the same warning from two branches and we could reduce code duplication with something like the following. However, I decided against that change because it doesn't really reduce overall complexity of the code.

def _detect_language(self, document: Document) -> str | None:
    language = None
    if document.content is not None:
        try:
            language = langdetect.detect(document.content)
        except langdetect.LangDetectException:
            pass
    if language is None:
        logger.warning(
            "Langdetect cannot detect the language of Document with id: {document_id}",
            document_id=document.id,
        )
    return language

[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
haystack/components/classifiers
document_language_classifier.py
Project Total

This report was generated by python-coverage-comment-action

[rautaditya2606]

Thanks for the review and the edits!

I also considered consolidating the warning logic similarly, but I agree that the current structure keeps the control flow a bit clearer without adding extra branching complexity. Appreciate the feedback and the merge.