[PR] Fix AwaitMessageTrigger crash on tombstone messages when apply_function is unset [airflow]

["TimurRakhmatullin86 (via GitHub)" <gi...@apache.org>]

TimurRakhmatullin86 opened a new pull request, #69665:
URL: https://github.com/apache/airflow/pull/69665

   When `AwaitMessageTrigger` is used without an `apply_function` (supported since #55437), the trigger calls `message.value().decode("utf-8")` on every polled message. For a tombstone message — `value()` is `None`, a routine occurrence on log-compacted topics where a null value is the deletion marker — this raises `AttributeError: 'NoneType' object has no attribute 'decode'`, crashing the trigger and failing the deferred task.
   
   This PR treats a tombstone the same way as any other non-matching message: no event is emitted, the offset is committed (when `commit_offset=True`, matching the existing non-matching path so the tombstone is not re-read forever after a restart), and the trigger keeps polling.
   
   Why skip rather than emit: the trigger's contract is already truthiness-based (`if event:`), so a `None` payload cannot be yielded on this path today, and a `TriggerEvent(None)` would carry no usable payload downstream. Users who need to react to tombstones can already do so via `apply_function`, which receives the raw message (including `value() is None`) and can map it to any truthy payload. Surfacing tombstones from the no-`apply_function` convenience path would be a separate opt-in feature; crashing on them is a bug.
   
   Tests:
   * `test_trigger_run_tombstone_message_keeps_polling` — regression test: `poll()` returns a null-value message; asserts the trigger neither raises nor yields and commits the tombstone offset. Fails on `main` with the exact `AttributeError` above.
   * `test_trigger_run_without_apply_function_yields_message_value` — asserts the happy path still yields the decoded payload.
   * `MockedMessage` now has a `value()` method: the `apply_function=None` case of `test_trigger_run_good` previously passed for the wrong reason — the mock lacked `value()`, so the task finished via this same `AttributeError`, satisfying `task.done() is True`.
   
   No behavior change for non-null messages or when `apply_function` is set. Empty (`b""`) payloads were already treated as non-events by the `if event:` check — unchanged.
   


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Re: [PR] Fix AwaitMessageTrigger crash on tombstone messages when apply_function is unset [airflow]

["potiuk (via GitHub)" <gi...@apache.org>]

potiuk merged PR #69665:
URL: https://github.com/apache/airflow/pull/69665


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