code: def test_fillna_parr(self):
      # GH-24537
      dti = date_range(
          Timestamp.max - Timedelta(nanoseconds=10),
          periods=5,
          freq="ns",
      )
      ser = Series(dti.to_period("ns"))
      ser[2] = NaT
      arr = period_array(
          [
              Timestamp("2262-04-11 23:47:16.854775797"),
              Timestamp("2262-04-11 23:47:16.854775798"),
              Timestamp("2262-04-11 23:47:16.854775798"),
              Timestamp("2262-04-11 23:47:16.854775800"),
              Timestamp("2262-04-11 23:47:16.854775801"),
          ],
          freq="ns",
      )
      expected = Series(arr)
  
      filled = ser.ffill()
  
      tm.assert_series_equal(filled, 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 10 for calling the TestFillnaPad obj's underlying member method code with example usage: obj.test_fillna_parr() without return types