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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def read_notes_file(file_path):
 """ Returns the contents of a notes file. If the notes file does not exist, None is returned """


    if not os.path.isfile(file_path):
        return None

    with open(file_path, 'r', encoding=_default_encoding) as f:
        return f.read()