code: def test_map_batches_preserves_empty_block_format(
      ray_start_regular_shared,
  ):
      """Tests that the block format for empty blocks are not modified."""
  
      def empty_pandas(batch):
          return pd.DataFrame({"x": []})
  
      df = pd.DataFrame({"x": [1, 2, 3]})
  
      # First map_batches creates the empty Pandas block.
      # Applying subsequent map_batches should not change the type of the empty block.
      ds = (
          ray.data.from_pandas(df)
          .map_batches(empty_pandas)
          .map_batches(lambda x: x, batch_size=None)
      )
  
      block_refs = ds.get_internal_block_refs()
      assert len(block_refs) == 1
      assert type(ray.get(block_refs[0])) == pd.DataFrame
  
imports: import itertools
  import math
  import os
  import signal
  import threading
  import time
  from typing import Iterator
  import numpy
  import pandas
  import pyarrow
  import pyarrow.parquet
  import pytest
  import ray
  from ray._private.test_utils import wait_for_condition
  from ray.data.block import BlockAccessor
  from ray.data.context import DataContext
  from ray.data.tests.conftest import *
  from ray.data.tests.util import column_udf, column_udf_class, extract_values
  from ray.tests.conftest import *
label_desc: Use image node_id 22 for calling a global function with example usage: test_map_batches_preserves_empty_block_format(ray_start_regular_shared) and returns: pd