code: def test_func_second_call_return_none(self):
      x = 1
  
      def f():
          return x
  
      logging_txt = free_vars_detect.generate_free_var_logging(f)
      self.assertIsNotNone(logging_txt)
      logging_txt = free_vars_detect.generate_free_var_logging(f)
      self.assertIsNone(logging_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 14 for calling the GenerateLoggingTest obj's underlying member method code with example usage: obj.test_func_second_call_return_none() and returns: x