code: def test_empty_map(backend):
      with BatchPoolExecutor(
          backend=backend, project="hail-vdc", image=PYTHON_DILL_IMAGE
      ) as bpe:
          actual = list(bpe.map(lambda x: x * 3, []))
      assert [] == actual
  
imports: import asyncio
  import time
  import pytest
  from hailtop.batch import BatchPoolExecutor, ServiceBackend
  from hailtop.config import get_user_config
  from hailtop.utils import sync_sleep_before_try
  from hailtop.batch_client.client import BatchClient
label_desc: Use image node_id 4 for calling a global function with example usage: test_empty_map(backend) without return types