Template generator fails with a single nested field

[annaghi]

If there is a single nested field without comment in a config, the template generator fails:

Output is invalid YAML:

nested:   one: true

Minimal example:

#[derive(Debug, Clone, Config, Serialize, Deserialize)]
pub struct ProjectConfig {
    #[setting(nested)]
    pub nested: NestedConfig,
}

#[derive(Debug, Clone, Config, Serialize, Deserialize)]
pub struct NestedConfig {
    #[setting(default = true)]
    pub one: bool,
}

fn generate_project_template(out_dir: &Path) -> Result<()> {
    let mut generator = SchemaGenerator::default();
    generator.add::<ProjectConfig>();

    generator
        .generate(out_dir.join("project.yml"), create_yaml_template_renderer())
        .map_err(|e| anyhow!("Template generation failed: {}", e))
        .with_context(|| "Failed to generate project template")?;

    Ok(())
}

fn create_yaml_template_renderer() -> YamlTemplateRenderer {
    YamlTemplateRenderer::new(TemplateOptions {
        ..TemplateOptions::default()
    })
}