code: def test_fillna_dt64_timestamp(self, frame_or_series):
      ser = Series(
          [
              Timestamp("20130101"),
              Timestamp("20130101"),
              Timestamp("20130102"),
              Timestamp("20130103 9:01:01"),
          ]
      )
      ser[2] = np.nan
      obj = frame_or_series(ser)
  
      # reg fillna
      result = obj.fillna(Timestamp("20130104"))
      expected = Series(
          [
              Timestamp("20130101"),
              Timestamp("20130101"),
              Timestamp("20130104"),
              Timestamp("20130103 9:01:01"),
          ]
      )
      expected = frame_or_series(expected)
      tm.assert_equal(result, expected)
  
      result = obj.fillna(NaT)
      expected = obj
      tm.assert_equal(result, 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 20 for calling the TestSeriesFillNA obj's underlying member method code with example usage: obj.test_fillna_dt64_timestamp(frame_or_series) without return types