Milvus expr fails when using $meta JSON path with boolean OR and null check

[xiaomayi-ant]

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Expression: ($meta["metadata"]["user_id"] == "UID" or $meta["metadata"]["user_id"] == null)
Error: failed to create query plan: cannot parse expression ... mismatched input 'OR' expecting ')'
Alternative tried: is null → mismatched input 'is' expecting ')'
Single equality (== "UID") works; failure occurs only when adding OR/null condition
Expected: expr should support boolean OR and null checks on $meta JSON fields
Repro: Collection.search(..., expr='($meta["metadata"]["user_id"] == "UID" or $meta["metadata"]["user_id"] == null)', output_fields=["$meta"])

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