code: def test_format_feature_mask_of_none(self) -> None:
      formatted_inputs = (
          torch.tensor([[0.0, 0.0], [0.0, 0.0]]),
          torch.tensor([]),  # empty tensor
          torch.tensor([[0.0, 0.0, 0.0], [0.0, 0.0, 0.0]]),
      )
  
      expected_mask = (
          torch.tensor([[0, 1]]),
          torch.tensor([]),
          torch.tensor([[2, 3, 4]]),
      )
      formatted_none_mask = _format_feature_mask(None, formatted_inputs)
  
      self.assertEqual(type(formatted_none_mask), tuple)
      assertTensorTuplesAlmostEqual(
          self, formatted_none_mask, expected_mask
      )
  
imports: from typing import cast, List, Tuple
  import torch
  from captum._utils.common import _format_feature_mask, _get_max_feature_index, _parse_version, _reduce_list, _select_targets, _sort_key_list, safe_div
  from tests.helpers.basic import assertTensorAlmostEqual, assertTensorTuplesAlmostEqual, BaseTest
label_desc: Use image node_id 11 for calling the Test obj's underlying member method code with example usage: obj.test_format_feature_mask_of_none() without return types