def validate_config(config)
        raise ConfigurationError, 'configuration is nil, did you forget to configure the gem?' unless config
        raise ConfigurationError, 'sftp_host must be configured' unless string_present? config.sftp_host
        raise ConfigurationError, 'sftp_user must be configured' unless string_present? config.sftp_user
        raise ConfigurationError, 'sftp_password must be configured' unless string_present? config.sftp_password