logger.go
func (opt *Options) Errorf(format string, v ...interface{}) {
	if opt.Logger == nil {
		return
	}
	opt.Logger.Errorf(format, v...)
}
func (opt *Options) Errorf(format string, v ...interface{}) {
	if opt.Logger == nil {
		return
	}
	opt.Logger.Errorf(format, v...)
}
// Errorf logs an ERROR log message to the logger specified in opts or to the
// global logger if no logger is specified in opts.