where assert

[muyids]

when I use ava --tab, the assert detail as follow

---
    operator: ===
    expected: 0
    actual: 202
    at: Test.<anonymous> (spec/my-code.js:34:5)
  ...

but, the tap-json just record as

{
    "extra": {
        "operator": "undefined",
        "expected": "undefined",
        "actual": "undefined"
    }
}

why didn't add the at info to extra ?