code: def test_all_null_cast_5826() -> None:
      df = pl.DataFrame(data=[pl.Series("a", [None], dtype=pl.String)])
      out = df.with_columns(pl.col("a").cast(pl.Boolean))
      assert out.dtypes == [pl.Boolean]
      assert out.item() is None
  
imports: from __future__ import annotations
  from collections import OrderedDict
  from datetime import date, timedelta
  from typing import Any, Iterator, Mapping
  import pytest
  import polars
  from polars.testing import assert_frame_equal, assert_series_equal
label_desc: Use image node_id 22 for calling a global function with example usage: test_all_null_cast_5826() without return types