code: def test_fillna_nones_inplace():
      # GH 48480
      df = DataFrame(
          [[None, None], [None, None]],
          columns=["A", "B"],
      )
      msg = "Downcasting object dtype arrays"
      with tm.assert_produces_warning(FutureWarning, match=msg):
          df.fillna(value={"A": 1, "B": 2}, inplace=True)
  
      expected = DataFrame([[1, 2], [1, 2]], columns=["A", "B"])
      tm.assert_frame_equal(df, expected)
  
imports: import numpy
  import pytest
  from pandas._config import using_pyarrow_string_dtype
  from pandas import Categorical, DataFrame, DatetimeIndex, NaT, PeriodIndex, Series, TimedeltaIndex, Timestamp, date_range, to_datetime
  import pandas._testing
  from pandas.tests.frame.common import _check_mixed_float
label_desc: Use image node_id 2 for calling a global function with example usage: test_fillna_nones_inplace() without return types