You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: id.go
    path of file: ./repos/juju/core/payloads
    
    the code of the file until where you have to start completion: // Copyright 2015 Canonical Ltd.
// Licensed under the AGPLv3, see LICENCE file for details.

package payloads

import (
	"strings"
)

// TODO(ericsnow) Add ValidateID()
    
func BuildID(class, id string) string {
	if id == "" {
		// TODO(natefinch) remove this special case when we can be sure the ID
		// is never empty (and fix the tests).
		return class
	}
	return class + "/" + id
}