code: def test_groupby_apply_timegrouper_with_nat_scalar_returns(
      self, groupby_with_truncated_bingrouper
  ):
      # GH#43500 Previously raised ValueError bc used index with incorrect
      #  length in wrap_applied_result
      gb = groupby_with_truncated_bingrouper
  
      res = gb["Quantity"].apply(
          lambda x: x.iloc[0] if len(x) else np.nan
      )
  
      df = gb.obj
      unit = df["Date"]._values.unit
      dti = date_range(
          "2013-09-01", "2013-10-01", freq="5D", name="Date", unit=unit
      )
      expected = Series(
          [18, np.nan, np.nan, np.nan, np.nan, np.nan, 5],
          index=dti._with_freq(None),
          name="Quantity",
      )
  
      tm.assert_series_equal(res, expected)
  
imports: from datetime import datetime, timedelta
  import numpy
  import pytest
  import pytz
  import pandas
  from pandas import DataFrame, DatetimeIndex, Index, MultiIndex, Series, Timestamp, date_range, offsets
  import pandas._testing
  from pandas.core.groupby.grouper import Grouper
  from pandas.core.groupby.ops import BinGrouper
label_desc: Use image node_id 25 for calling the TestGroupBy obj's underlying member method code with example usage: obj.test_groupby_apply_timegrouper_with_nat_scalar_returns(groupby_with_truncated_bingrouper) without return types