code: def test_empty_sample(self):
      # test sample with empty string and empty list
      self.assertRaises(AttributeError, nli_length.transform, "")
      self.assertRaises(AttributeError, nli_length.transform, [])
  
file_path: textflint/test/generation/transformation/NLI/test_add_sent.py
imports: import unittest
  from textflint.input.component.sample.nli_sample import NLISample
  from textflint.generation.transformation.NLI import AddSent
label_desc: Use image node_id 4 for calling the TestNliLength obj's underlying member method code with example usage: obj.test_empty_sample() without return types