code: func HeadersWithSpan(headers tasks.Headers, span opentracing.Span) tasks.Headers {
  	// check if the headers aren't nil
  	if headers == nil {
  		headers = make(tasks.Headers)
  	}
  
  	if err := opentracing.GlobalTracer().Inject(span.Context(), opentracing.TextMap, headers); err != nil {
  		span.LogFields(opentracing_log.Error(err))
  	}
  
  	return headers
  }
docs: // HeadersWithSpan will inject a span into the signature headers