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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 _resolve_file(file_name):
 """ Checks if the file exists. If the file exists, the method returns its absolute path. Else, it returns None :param file_name: The name of the file to check :return: An absolute path, or None """

    if not file_name:
        return None

    path = os.path.realpath(file_name)
    if os.path.isfile(path):
        return path

    return None