code: def _get_expected_exception(self, op_name, obj, other):
      if op_name in ("__sub__", "__rsub__"):
          return None
      return super()._get_expected_exception(op_name, obj, other)
  
imports: from __future__ import annotations
  from typing import TYPE_CHECKING
  import numpy
  import pytest
  from pandas._libs import Period, iNaT
  from pandas.compat import is_platform_windows
  from pandas.compat.numpy import np_version_gte1p24
  from pandas.core.dtypes.dtypes import PeriodDtype
  import pandas._testing
  from pandas.core.arrays import PeriodArray
  from pandas.tests.extension import base
label_desc: Use image node_id 1 for calling the TestPeriodArray obj's underlying member method code with example usage: obj._get_expected_exception(op_name, obj, other) and returns: super, None