Replace deprecated DummyOperator by EmptyOperator if Airflow >=2.4.0 (a…

…stronomer#900)

Change the example of customising Cosmos operators to use `EmptyOperator`,
since the `DummyOperator` was deprecated in Airflow 2.4.

dev/dags/example_cosmos_sources.py

@@ -17,7 +17,11 @@
 from pathlib import Path
 
 from airflow.models.dag import DAG
-from airflow.operators.dummy import DummyOperator
+
+try:  # available since Airflow 2.4.0
+    from airflow.operators.empty import EmptyOperator
+except ImportError:
+    from airflow.operators.dummy import DummyOperator as EmptyOperator
 from airflow.utils.task_group import TaskGroup
 
 from cosmos import DbtDag, ProfileConfig, ProjectConfig, RenderConfig
@@ -38,21 +42,21 @@
 
 
 # [START custom_dbt_nodes]
-# Cosmos will use this function to generate a DummyOperator task when it finds a source node, in the manifest.
+# Cosmos will use this function to generate an empty task when it finds a source node, in the manifest.
 # A more realistic use case could be to use an Airflow sensor to represent a source.
 def convert_source(dag: DAG, task_group: TaskGroup, node: DbtNode, **kwargs):
     """
-    Return an instance of DummyOperator to represent a dbt "source" node.
+    Return an instance of a desired operator to represent a dbt "source" node.
     """
-    return DummyOperator(dag=dag, task_group=task_group, task_id=f"{node.name}_source")
+    return EmptyOperator(dag=dag, task_group=task_group, task_id=f"{node.name}_source")
 
 
-# Cosmos will use this function to generate a DummyOperator task when it finds a exposure node, in the manifest.
+# Cosmos will use this function to generate an empty task when it finds a exposure node, in the manifest.
 def convert_exposure(dag: DAG, task_group: TaskGroup, node: DbtNode, **kwargs):
     """
-    Return an instance of DummyOperator to represent a dbt "exposure" node.
+    Return an instance of a desired operator to represent a dbt "exposure" node.
     """
-    return DummyOperator(dag=dag, task_group=task_group, task_id=f"{node.name}_exposure")
+    return EmptyOperator(dag=dag, task_group=task_group, task_id=f"{node.name}_exposure")
 
 
 # Use `RenderConfig` to tell Cosmos, given a node type, how to convert a dbt node into an Airflow task or task group.