code: def test_fillna_consistency(self):
      # GH#16402
      # fillna with a tz aware to a tz-naive, should result in object
  
      ser = Series([Timestamp("20130101"), NaT])
  
      result = ser.fillna(Timestamp("20130101", tz="US/Eastern"))
      expected = Series(
          [
              Timestamp("20130101"),
              Timestamp("2013-01-01", tz="US/Eastern"),
          ],
          dtype="object",
      )
      tm.assert_series_equal(result, expected)
  
      result = ser.where(
          [True, False], Timestamp("20130101", tz="US/Eastern")
      )
      tm.assert_series_equal(result, expected)
  
      result = ser.where(
          [True, False], Timestamp("20130101", tz="US/Eastern")
      )
      tm.assert_series_equal(result, expected)
  
      # with a non-datetime
      result = ser.fillna("foo")
      expected = Series([Timestamp("20130101"), "foo"])
      tm.assert_series_equal(result, expected)
  
      # assignment
      ser2 = ser.copy()
      with tm.assert_produces_warning(
          FutureWarning, match="incompatible dtype"
      ):
          ser2[1] = "foo"
      tm.assert_series_equal(ser2, expected)
  
imports: from datetime import datetime, timedelta, timezone
  import numpy
  import pytest
  import pytz
  from pandas import Categorical, DataFrame, DatetimeIndex, NaT, Period, Series, Timedelta, Timestamp, date_range, isna, timedelta_range
  import pandas._testing
  from pandas.core.arrays import period_array
label_desc: Use image node_id 8 for calling the TestSeriesFillNA obj's underlying member method code with example usage: obj.test_fillna_consistency() without return types