code: def test_all_nans(self):
      # GH 15713
      # series is all nans
  
      # testing non-default indexes
      N = 50
      rng = date_range("1/1/1990", periods=N, freq="53s")
  
      dates = date_range("1/1/1990", periods=N * 3, freq="25s")
      result = Series(np.nan, index=rng).asof(dates)
      expected = Series(np.nan, index=dates)
      tm.assert_series_equal(result, expected)
  
      # testing scalar input
      date = date_range("1/1/1990", periods=N * 3, freq="25s")[0]
      result = Series(np.nan, index=rng).asof(date)
      assert isna(result)
  
      # test name is propagated
      result = Series(np.nan, index=[1, 2, 3, 4], name="test").asof(
          [4, 5]
      )
      expected = Series(np.nan, index=[4, 5], name="test")
      tm.assert_series_equal(result, expected)
  
file_path: pandas/pandas/tests/series/methods/test_asof.py
imports: import numpy
  import pytest
  from pandas._libs.tslibs import IncompatibleFrequency
  from pandas import DatetimeIndex, PeriodIndex, Series, Timestamp, date_range, isna, notna, offsets, period_range
  import pandas._testing
label_desc: Use image node_id 7 for calling the TestSeriesAsof obj's underlying member method code with example usage: obj.test_all_nans() without return types