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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 create(cls, config_file=None):
 """ Return the default configuration. """

        if cls.instance is None:
            cls.instance = cls(config_file)

            # Load config file, possibly overwriting the defaults
            cls.instance.load_ini()

        if config_file and config_file != cls.instance.config_file:
            raise RuntimeError("Configuration initialized a second time with a different file!")

        return cls.instance