docstr: 测试 path 是 None；
docstr_tok: ["\u6d4b\u8bd5","path","\u662f","None\uff1b"]
code: def test_add_file_3(self):
      """
      测试 path 是 None；
      """
      handler = logger.add_file()
      logger.info(self.msg)
  
      path = Path.cwd()
      cur_datetime = str(datetime.datetime.now().strftime("%Y-%m-%d"))
      for file in path.iterdir():
          if file.name.startswith(cur_datetime):
              with open(file, "r") as f:
                  line = "".join([l for l in f])
              assert self.msg in line
              file.unlink()
  
imports: import os
  import tempfile
  import datetime
  from pathlib import Path
  import logging
  import re
  import pytest
  from fastNLP.envs.env import FASTNLP_LAUNCH_TIME
  from fastNLP.envs.distributed import rank_zero_rm
  from fastNLP.core.log.logger import logger
  from tests.helpers.utils import magic_argv_env_context, recover_logger
label_desc: Use image node_id 3 for calling the TestLogger obj's underlying member method code with example usage: obj.test_add_file_3() without return types