code: def test_insert_nat(self, null):
      # GH 18295 (test missing)
      idx = timedelta_range("1day", "3day")
      result = idx.insert(1, null)
      expected = TimedeltaIndex(["1day", pd.NaT, "2day", "3day"])
      tm.assert_index_equal(result, expected)
  
file_path: pandas/pandas/tests/indexes/timedeltas/methods/test_insert.py
imports: from datetime import timedelta
  import numpy
  import pytest
  from pandas._libs import lib
  import pandas
  from pandas import Index, Timedelta, TimedeltaIndex, timedelta_range
  import pandas._testing
label_desc: Use image node_id 2 for calling the TestTimedeltaIndexInsert obj's underlying member method code with example usage: obj.test_insert_nat(null) without return types