FallbackDir: Do not consider defaulted-empty orport list to be valid

    }

    /// Check whether this builder is ready to make a FallbackDir.

    fn validate(&self) -> std::result::Result<(), ConfigBuildError> {

        if let Some(orports) = &self.orports {

            if orports.is_empty() {

        if ! self.orports.as_ref().map(|l| !l.is_empty()).unwrap_or(false) {

            return Err(ConfigBuildError::Invalid {

                field: "orport".to_string(),

                problem: "list was empty".to_string(),

            });

        }

        }

        Ok(())

    }

}