code: def test_list_fill_list() -> None:
      assert pl.DataFrame({"a": [[1, 2, 3], []]}).select(
          [
              pl.when(pl.col("a").list.len() == 0)
              .then([5])
              .otherwise(pl.col("a"))
              .alias("filled")
          ]
      ).to_dict(as_series=False) == {"filled": [[1, 2, 3], [5]]}
  
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 6 for calling a global function with example usage: test_list_fill_list() without return types