code: def str_mapping() -> dict[str | None, str]:
      return {
          "CA": "Canada",
          "DE": "Germany",
          "FR": "France",
          None: "Not specified",
      }
  
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 1 for calling a global function with example usage: str_mapping() and returns: dict