fix: Pass empty list instead of None when headers are empty (#211)

minioevents.py

@@ -114,7 +114,7 @@ def _key_mapper(ce: CloudEvent) -> Any | None:  # noqa: ANN401
                 producer_topic,
                 key=km.key,
                 value=km.value,
-                headers=km.headers if km.headers else None,
+                headers=km.headers if km.headers else [],
             ).add_errback(on_send_error)
         producer.flush()