fix(kafka): do identity checks on kafka messages to work around... [backport 2.7] (#8712)

This pull request fixes
#8602 by changing `if
message` tests in the Kafka contrib to `if message is not None`. This
avoids the runtime calling `__len__` on the message object, which is not
guaranteed by confluent-kafka to be defined.

## Checklist

- [x] Change(s) are motivated and described in the PR description
- [x] Testing strategy is described if automated tests are not included
in the PR
- [x] Risks are described (performance impact, potential for breakage,
maintainability)
- [x] Change is maintainable (easy to change, telemetry, documentation)
- [x] [Library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
are followed or label `changelog/no-changelog` is set
- [x] Documentation is included (in-code, generated user docs, [public
corp docs](https://github.com/DataDog/documentation/))
- [x] Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))
- [x] If this PR changes the public interface, I've notified
`@DataDog/apm-tees`.
- [x] If change touches code that signs or publishes builds or packages,
or handles credentials of any kind, I've requested a review from
`@DataDog/security-design-and-guidance`.

## Reviewer Checklist

- [x] Title is accurate
- [x] All changes are related to the pull request's stated goal
- [x] Description motivates each change
- [x] Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- [x] Testing strategy adequately addresses listed risks
- [x] Change is maintainable (easy to change, telemetry, documentation)
- [x] Release note makes sense to a user of the library
- [x] Author has acknowledged and discussed the performance implications
of this PR as reported in the benchmarks PR comment
- [x] Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

Co-authored-by: Tahir H. Butt <[email protected]>

Author: emmettbutler

ddtrace/contrib/kafka/patch.py

@@ -209,9 +209,9 @@ def traced_poll(func, instance, args, kwargs):
     except Exception as e:
         err = e
     ctx = None
-    if message and config.kafka.distributed_tracing_enabled and message.headers():
+    if message is not None and config.kafka.distributed_tracing_enabled and message.headers():
         ctx = Propagator.extract(dict(message.headers()))
-    if message or config.kafka.trace_empty_poll_enabled:
+    if message is not None or config.kafka.trace_empty_poll_enabled:
         with pin.tracer.start_span(
             name=schematize_messaging_operation(kafkax.CONSUME, provider="kafka", direction=SpanDirection.PROCESSING),
             service=trace_utils.ext_service(pin, config.kafka),

releasenotes/notes/kafka-none-2-4f9e600e115eb44c.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    kafka: This fix resolves an issue where ``None`` messages from confluent-kafka could cause crashes in the Kafka integration.