fix(tracing): preserve empty-string metadata values

[i-anubhav-anand]

Empty-string metadata values are silently dropped. In _flattenAndSerializeMetadata:

const serialized = typeof value === "string" ? value : _serialize(value);
if (serialized) {                       // "" is falsy -> dropped
  metadataAttributes[`${prefix}.${key}`] = serialized;
}

So metadata: { a: "", b: "x", c: 0, d: false } emits b, c ("0"), d ("false") but silently drops a — inconsistent, since 0 and false survive.

_serialize returns undefined only for null/undefined, so switching the guard to if (serialized !== undefined) preserves "" (and any other falsy-but-present value) while still skipping null/undefined. Applied to both the scalar-metadata branch and the object-entry loop.

Test

Adds an integration test (tracing.integration.test.ts) asserting an empty-string metadata value is exported. Fails before (attribute absent), passes after. prettier/eslint/tsc clean (pre-commit hook).

Type of change

• Bug fix (non-breaking change which fixes an issue)

Greptile Summary

This PR fixes a silent data-loss bug in _flattenAndSerializeMetadata where empty-string metadata values ("") were dropped because the truthiness guard if (serialized) evaluated "" as falsy. The fix changes both guards to serialized !== undefined, which aligns with _serialize's contract of returning undefined only for null/undefined inputs.

• packages/tracing/src/attributes.ts: Two if (serialized) guards replaced with if (serialized !== undefined) in the scalar and object-entry branches of _flattenAndSerializeMetadata.
• tests/integration/tracing.integration.test.ts: Integration test added that verifies an empty-string metadata value appears as a span attribute after export.

Confidence Score: 5/5

Safe to merge — the change is a minimal, targeted guard fix that preserves existing behavior for all non-empty values while correctly retaining empty strings.

The two-line change is narrowly scoped: _serialize is guaranteed to return either a string or undefined, so !== undefined is the correct predicate. All previously-passing values (non-empty strings, numbers, booleans, objects) continue to pass the new guard unchanged, and only the previously-dropped "" case is now correctly preserved. The integration test directly validates the fixed scenario.

No files require special attention — both changed files are straightforward and self-contained.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["_flattenAndSerializeMetadata(metadata, type)"] --> B{metadata null/undefined?}
    B -- Yes --> C[return empty object]
    B -- No --> D{Is metadata non-object or Array?}
    D -- Yes --> E["serialized = _serialize(metadata)"]
    E --> F{"serialized !== undefined?\n(was: if serialized)"}
    F -- Yes --> G["metadataAttributes[prefix] = serialized"]
    F -- No --> C
    D -- No --> H["for each [key, value] in metadata"]
    H --> I{"typeof value === 'string'?"}
    I -- Yes --> J["serialized = value (direct, e.g. '')"]    
    I -- No --> K["serialized = _serialize(value)"]
    J --> L{"serialized !== undefined?\n(was: if serialized — dropped '')"}
    K --> L
    L -- Yes --> M["metadataAttributes[prefix.key] = serialized"]
    L -- No --> H
    G --> N[return metadataAttributes]
    M --> N

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