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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 file_config(filename=None):
 """Returns the config values found in a configuration file. Args: filename (str):
 the JSON file with the configuration values. If ``None``, CONFIG_DEFAULT_PATH will be used. Returns: dict: The config values in the specified config file (or the file at CONFIG_DEFAULT_PATH, if filename == None) """

    logger.debug('On entry into file_config(), filename = {}'.format(filename))

    if filename is None:
        filename = CONFIG_DEFAULT_PATH

    logger.debug('file_config() will try to open `{}`'.format(filename))
    with open(filename) as f:
        try:
            config = json.load(f)
        except ValueError as err:
            raise exceptions.ConfigurationError(
                'Failed to parse the JSON configuration from `{}`, {}'.format(filename, err)
            )

        logger.info('Configuration loaded from `{}`'.format(filename))

    return config