code: func (p *PrometheusReporter) ensureLabels(labels map[string]string) map[string]string {
  	for key, defaultVal := range p.additionalLabels {
  		if _, ok := labels[key]; !ok {
  			labels[key] = defaultVal
  		}
  	}
  
  	return labels
  }
docs: // ensureLabels checks if labels contains the additionalLabels values,
  // otherwise adds them with the default values