code: def test_fill_null_empty_list() -> None:
      assert pl.Series([["a"], None]).fill_null([]).to_list() == [
          ["a"],
          [],
      ]
  
imports: from __future__ import annotations
  import pickle
  from datetime import date, datetime, time
  from typing import TYPE_CHECKING, Any
  import pandas
  import pytest
  import polars
  from polars.testing import assert_frame_equal, assert_series_equal
label_desc: Use image node_id 24 for calling a global function with example usage: test_fill_null_empty_list() without return types