code: def test_timedelta64_fillna_mismatched_reso_no_rounding(self, scalar):
      # GH#56410
      tdi = date_range("2016-01-01", periods=3, unit="s") - Timestamp(
          "1970-01-01"
      )
      item = Timestamp("2016-02-03 04:05:06.789") - Timestamp(
          "1970-01-01"
      )
      vec = timedelta_range(item, periods=3, unit="ms")
  
      expected = Series([item, tdi[1], tdi[2]], dtype="m8[ms]")
  
      ser = Series(tdi)
      ser[0] = NaT
      ser2 = ser.copy()
  
      res = ser.fillna(item)
      res2 = ser2.fillna(Series(vec))
  
      if scalar:
          tm.assert_series_equal(res, expected)
      else:
          tm.assert_series_equal(res2, 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 14 for calling the TestSeriesFillNA obj's underlying member method code with example usage: obj.test_timedelta64_fillna_mismatched_reso_no_rounding(scalar) without return types