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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 get(self, key: str) -> Optional[str]: """ Returns an optional configuration value by its key, or None if it doesn't exist. :param str key: The requested configuration key. :return: The configuration key's value, or None if one does not exist. :rtype: Optional[str] """

        return get_config(self.full_key(key))