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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 _validate_config(config_path):
    '''
    Validate that the configuration file exists and is readable.

    :param str config_path: The path to the configuration file for the aptly instance.

    :return: None
    :rtype: None
    '''
    log.debug('Checking configuration file: %s', config_path)

    if not os.path.isfile(config_path):
        message = 'Unable to get configuration file: {}'.format(config_path)
        log.error(message)
        raise SaltInvocationError(message)
    log.debug('Found configuration file: %s', config_path)