code: def test_xcom_map_transform_to_none(dag_maker, session):
      results = set()
  
      with dag_maker(session=session) as dag:
  
          @dag.task()
          def push():
              return ["a", "b", "c"]
  
          @dag.task()
          def pull(value):
              results.add(value)
  
          def c_to_none(v):
              if v == "c":
                  return None
              return v
  
          pull.expand(value=push().map(c_to_none))
  
      dr = dag_maker.create_dagrun(session=session)
  
      # Run "push".
      decision = dr.task_instance_scheduling_decisions(session=session)
      for ti in decision.schedulable_tis:
          ti.run(session=session)
  
      # Run "pull". This should automatically convert "c" to None.
      decision = dr.task_instance_scheduling_decisions(session=session)
      for ti in decision.schedulable_tis:
          ti.run(session=session)
      assert results == {"a", "b", None}
  
file_path: airflow/tests/models/test_xcom_arg_map.py
imports: from __future__ import annotations
  import pytest
  from airflow.exceptions import AirflowSkipException
  from airflow.utils.state import TaskInstanceState
  from airflow.utils.trigger_rule import TriggerRule
label_desc: Use image node_id 2 for calling a global function with example usage: test_xcom_map_transform_to_none(dag_maker, session) and returns: list, v, None