code: def test_replace_int_to_str_with_null() -> None:
      df = pl.DataFrame(
          {"int": [None, 1, None, 3]}, schema={"int": pl.Int16}
      )
      mapping = {1: "b", 3: "d", None: "e"}
      result = df.select(replaced=pl.col("int").replace(mapping))
      expected = pl.DataFrame({"replaced": ["e", "b", "e", "d"]})
      assert_frame_equal(result, expected)
  
imports: from __future__ import annotations
  import contextlib
  from typing import Any
  import pytest
  import polars
  from polars.exceptions import CategoricalRemappingWarning
  from polars.testing import assert_frame_equal, assert_series_equal
label_desc: Use image node_id 15 for calling a global function with example usage: test_replace_int_to_str_with_null() without return types