python ValueError: source code string cannot contain null bytes

pytest executes test cases with the following error

(python) D:\study\python\BasicKnowledgePoints\s5_frame\f01_pytest\f004_conftest>pytest test_01.py
ImportError while loading conftest 'D:\study\python\BasicKnowledgePoints\s5_frame\f01_pytest\f004_conftest\conftest.py'.
ValueError: source code string cannot contain null bytes

the reason is that my D:\study\python\BasicKnowledgePoints\s5_frame\f01_pytest\ init

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