DAG import error after v3 upgrade

Hi community, I run into the same error after Airflow was upgraded to version 3, and worked around it by updating the `dag_id` parameter with a different value. I did delete all entries in `serialized_dag` table but not `dag_code` table. I guess both ways may trigger the same logic in the codes to work around the error. Just to see if someone happens to know the cause. > Is there a way to fix this manually? > > airflow db migrate was failing (no dag_id in the dag_code table). I ended up deleting rows in the dag_code and serialized_dag tables but now my DAG processor has these errors: > > ``` > latest_ser_dag._data = new_serialized_dag._data > ^^^^^^^^^^^^^^^^^^^^ > AttributeError: 'NoneType' object has no attribute '_data' > ``` > > I tried entering the dag processor pod and running `airflow dags reserialize` but no luck. If you have access to DB, truncate `dag_code` and `serialized_dag` table. _Originally posted by @kaxil in https://github.com/apache/airflow/issues/49563#issuecomment-2857985521_