Fix execution failures with NULL dag_run.conf during upgrades

[kaxil]

Task execution and scheduler operations failed when processing dag runs with NULL conf values in the database. This occurred during Airflow 2.x to 3.x upgrades where existing running DAG runs had NULL conf, and when clearing dag runs that were migrated with NULL conf during offline migrations.

The execution API DagRun datamodel required conf to be a dict, but the database schema allows NULL. This fix makes the conf field nullable to match the database schema, Core API datamodel, and Task SDK expectations.

For backward compatibility, older API versions (pre-2025-10-10) will receive an empty dict instead of None when conf is NULL.

Fixes#56707
Fixes#56705

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[ephraimbuddy]

What do you think about my approach here: https://github.com/apache/airflow/pull/55884/files#diff-680cf6d70e96761db3869142642ba1df32e5c2c5c8d1b9ab65d0200dca4718daR229

[kaxil]

What do you think about my approach here: https://github.com/apache/airflow/pull/55884/files#diff-680cf6d70e96761db3869142642ba1df32e5c2c5c8d1b9ab65d0200dca4718daR229

Oh I hadn't seen that PR. The generated Task SDK client already accepts None & DB accepts null values -- so it just made sense to make it consistent -- than to have to coerce it everywhere null is passed:

airflow/task-sdk/src/airflow/sdk/api/datamodels/_generated.py

Line 541 in c0f9d11

conf: Annotated[dict[str, Any] |None, Field(title="Conf")] =None

[tirkarthi]

IMO, it will be good to have the db and models in sync. Similar report with our migration #50386 .

[kaxil]

Yeah, this PR makes it consistent. Could I get a review @tirkarthi

[kaxil]

(k8s failure fixed in #56733)

[gopidesupavan]

LGTM :)

[github-actions]

Backport failed to create: v3-1-test. View the failure log Run details

Status	Branch	Result
❌	v3-1-test

You can attempt to backport this manually by running:

cherry_picker 0815019 v3-1-test

This should apply the commit to the v3-1-test branch and leave the commit in conflict state marking
the files that need manual conflict resolution.

After you have resolved the conflicts, you can continue the backport process by running:

cherry_picker --continue

[tirkarthi]

Thanks @kaxil