code: func getParentId(md metadata.Metadata) string {
  	// try as is
  	if h, ok := md[awsxray.TraceHeader]; ok {
  		return awsxray.GetParentId(h)
  	}
  
  	// try lower case
  	if h, ok := md[strings.ToLower(awsxray.TraceHeader)]; ok {
  		return awsxray.GetParentId(h)
  	}
  
  	return ""
  }
docs: // getParentId returns parent header or blank