func Code(err error) ErrCode {
	if err == nil {
		return OK
	}

	hte, ok := err.(*hashTreeError)
	if !ok {
		return Unknown
	}
	return hte.code
}
func Code(err error) ErrCode {
	if err == nil {
		return OK
	}

	hte, ok := err.(*hashTreeError)
	if !ok {
		return Unknown
	}
	return hte.code
}
// Code returns the "error code"  of 'err' if it was returned by one of the
// HashTree methods, or "Unknown" if 'err' was emitted by some other function
// (error codes are defined in interface.go)