code: def test_union_freq_both_none(self, sort):
      # GH11086
      expected = bdate_range("20150101", periods=10)
      expected._data.freq = None
  
      result = expected.union(expected, sort=sort)
      tm.assert_index_equal(result, expected)
      assert result.freq is None
  
imports: from datetime import datetime, timezone
  import numpy
  import pytest
  import pytz
  import pandas.util._test_decorators
  import pandas
  from pandas import DataFrame, DatetimeIndex, Index, Series, Timestamp, bdate_range, date_range
  import pandas._testing
  from pandas.tseries.offsets import BMonthEnd, Minute, MonthEnd
label_desc: Use image node_id 8 for calling the TestDatetimeIndexSetOps obj's underlying member method code with example usage: obj.test_union_freq_both_none(sort) without return types