fix: return empty string for empty filter list in parse_metadata_filters_recursive

[evanerwee]

Summary

When MetadataFilters has an empty filters list, parse_metadata_filters_recursive returns "()" (from joining an empty list within parentheses). This truthy string bypasses the guard in VersionManager._get_existing_source_nodes() at line 70:

if not where_clauses:  # "()" is truthy — guard fails
    return []

This causes the VersionManager to generate invalid Cypher:

WHERE () AND coalesce(source.__aws__versioning__id_fields__, ...) = $param

Neptune Database (1.4.7.0) rejects this with:

MalformedQueryException: Invalid input 'A': expected whitespace, comment or a relationship pattern

Fix

Return '' (empty string) when filter_strs is empty, before reaching the condition-based join logic.

if not filter_strs:
    return ''

Testing

• Added 2 unit tests covering empty filter lists with AND and OR conditions
• Verified on Neptune Database 1.4.7.0: the versioning query now works correctly
• Confirmed via direct Neptune query testing that Neptune supports all other Cypher features used by the VersionManager (map literals, coalesce, __ property names)

Evidence

Direct Neptune testing results (from issue #408):

Test	Query Pattern	Result
Map literal in RETURN	RETURN {id: id(n)} AS result	✅ Works
__aws__ property names	t.__aws__versioning__id_fields__	✅ Works
coalesce on versioning properties	coalesce(t.__aws__versioning__valid_from__, -1)	✅ Works
WHERE () AND filter	WHERE () AND id(n) IS NOT NULL	❌ MalformedQueryException
Full versioning query (properly formed)	Complete pattern with valid WHERE	✅ Works

Fixes #408

[mykola-pereyma]

LGTM. Thank you!

[oussamahansal]

@evanerwee Can you please resolve the conflict and rebase before we merge it. Thank you!