fix: accept zero hierarchy meta values in AutoMergingRetriever

[coder058]

Related Issues

• fixes AutoMergingRetriever treats __level=0 / __block_size=0 as missing metadata #12634

Proposed Changes:

AutoMergingRetriever._check_valid_documents validated __level and __block_size with truthiness (doc.meta.get(...)), so a present value of 0 was treated as missing.

HierarchicalDocumentSplitter intentionally stores __level=0 and __block_size=0 on the root document. Validation now checks key presence (__level in doc.meta) instead of truthiness. __parent_id` still requires a truthy value because leaves must point at a parent.

How did you test it?

• Added test_run_accepts_zero_level_and_block_size.
• Confirmed the new test fails on unmodified main without this patch (ValueError: ... '__level').
• Confirmed the new test passes with the patch.
• Ran the full AutoMergingRetriever unit suite: hatch -e test run pytest test/components/retrievers/test_auto_merging_retriever.py → 20 passed.

Notes for the reviewer

• Smallest change is confined to _check_valid_documents (shared by sync and async paths).
• Recent committers on this file: @anakin87 @julian-risch @davidsbatista

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: fix:
• I have documented my code.
• I have added a release note file, following the contributors guidelines.
• I have run relevant tests and fixed any issue.

This PR was fully generated with an AI assistant. I have reviewed the changes and run the relevant tests.

[vercel]

@coder058 is attempting to deploy a commit to the deepset Team on Vercel.

A member of the Team first needs to authorize it.

[CLAassistant]

All committers have signed the CLA.

[sjrl]

Thanks!

[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
haystack/components/retrievers
auto_merging_retriever.py
filter_retriever.py
Project Total

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