code: def test_nested_null_roundtrip() -> None:
      f = io.BytesIO()
      df = pl.DataFrame(
          {
              "experiences": [
                  [
                      {"company": "Google", "years": None},
                      {"company": "Facebook", "years": None},
                  ],
              ]
          }
      )
  
      df.write_parquet(f)
      f.seek(0)
      df_read = pl.read_parquet(f)
      assert_frame_equal(df_read, df)
  
imports: from __future__ import annotations
  import io
  from datetime import datetime, time, timezone
  from decimal import Decimal
  from typing import TYPE_CHECKING
  import numpy
  import pandas
  import pyarrow
  import pyarrow.dataset
  import pyarrow.parquet
  import pytest
  import polars
  from polars.testing import assert_frame_equal, assert_series_equal
label_desc: Use image node_id 25 for calling a global function with example usage: test_nested_null_roundtrip() without return types