func IsUserNotFound(err error) bool {
	if ae, ok := err.(authError); ok {
		return userNotFoundRegExp.MatchString(ae.Message)
	}
	return false
}
func IsUserNotFound(err error) bool {
	if ae, ok := err.(authError); ok {
		return userNotFoundRegExp.MatchString(ae.Message)
	}
	return false
}
// IsUserNotFound returns true if the error means user not found of v2 API.