Serialize dag if it is not serialized even if it does not have task instances

airflow-core/src/airflow/models/serialized_dag.py

@@ -723,7 +723,7 @@ def write_dag(
                 )
             )
 
-        if dag_version and not has_task_instances:
+        if dag_version and not has_task_instances and serialized_dag_hash is not None:
             # This is for dynamic DAGs that the hashes changes often. We should update
             # the serialized dag, the dag_version and the dag_code instead of a new version
             # if the dag_version is not associated with any task instances

airflow-core/tests/unit/models/test_serialized_dag.py

@@ -772,10 +772,12 @@ def __init__(self, *, task_id: str, **kwargs):
         # Hashes should be identical
         assert hash_1 == hash_2, "Hashes should be identical when dicts are sorted consistently"
 
-    def test_dynamic_dag_update_preserves_null_check(self, dag_maker, session):
+    def test_new_dag_version_is_created_when_version_exists_but_serialized_dag_row_missing(
+        self, dag_maker, session
+    ):
         """
         Test that dynamic DAG update gracefully handles case where SerializedDagModel doesn't exist.
-        This preserves the null-check fix from PR #56422 and tests the direct UPDATE path.
+        This adds the serialized dag entry
         """
         with dag_maker(dag_id="test_missing_serdag", serialized=True, session=session) as dag:
             EmptyOperator(task_id="task1")
@@ -803,16 +805,19 @@ def test_dynamic_dag_update_preserves_null_check(self, dag_maker, session):
         # Verify no SerializedDagModel exists
         assert SDM.get("test_missing_serdag", session=session) is None
 
-        # Try to update - should return False gracefully (not crash)
+        # Try to update - should create the serialized dag
         result = SDM.write_dag(
             dag=lazy_dag,
             bundle_name="test_bundle",
             bundle_version=None,
             min_update_interval=None,
             session=session,
         )
+        session.commit()
 
-        assert result is False  # Should return False when SerializedDagModel is missing
+        serialized_dag = session.scalar(select(SDM).where(SDM.dag_id == "test_missing_serdag").limit(1))
+        assert serialized_dag is not None
+        assert result is True
 
     def test_dynamic_dag_update_success(self, dag_maker, session):
         """