code: func Get(names ...string) (map[string]string, error) {
  	values := map[string]string{}
  
  	var missingEnvVars []string
  	for _, envVar := range names {
  		value := GetOrFile(envVar)
  		if value == "" {
  			missingEnvVars = append(missingEnvVars, envVar)
  		}
  		values[envVar] = value
  	}
  
  	if len(missingEnvVars) > 0 {
  		return nil, fmt.Errorf("some credentials information are missing: %s", strings.Join(missingEnvVars, ","))
  	}
  
  	return values, nil
  }
docs: // Get environment variables