code: def test_none_input(self):
      txt = free_vars_detect.generate_free_var_logging(None)
      self.assertIsNone(txt)
  
imports: import functools
  import unittest
  from absl.testing import parameterized
  import numpy
  from tensorflow.core.function.capture import free_vars_detect
  from tensorflow.python.util import tf_decorator
label_desc: Use image node_id 2 for calling the GenerateLoggingTest obj's underlying member method code with example usage: obj.test_none_input() without return types