code: def _empty_input_for_insert(self):
      texts = [" "]
      aug = naw.TfIdfAug(
          model_path=os.environ.get("MODEL_DIR"),
          action=Action.SUBSTITUTE,
      )
  
      for text in texts:
          augmented_data = aug.augment(text)
          augmented_text = augmented_data[0]
  
          self.assertEqual("", augmented_text)
  
      self.assertEqual(1, len(texts))
  
file_path: nlpaug/test/augmenter/word/test_tfidf.py
imports: import unittest
  import os
  import re
  from dotenv import load_dotenv
  import sklearn.datasets
  import nlpaug.augmenter.word
  import nlpaug.model.word_stats
  from nlpaug.util import Action
label_desc: Use image node_id 5 for calling the TestTfIdf obj's underlying member method code with example usage: obj._empty_input_for_insert() without return types