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: cookie.go
    path of file: ./repos/sliver/implant/vendor/github.com/BurntSushi/xgb
    
    the code of the file until where you have to start completion: package xgb

import (
	"errors"
)

// Cookie is the internal representation of a cookie, where one is generated
// for *every* request sent by XGB.
// 'cookie' is most frequently used by em
    
func (c Cookie) replyUnchecked() ([]byte, error) {
	if c.replyChan == nil {
		return nil, errors.New("Cannot call 'replyUnchecked' on a cookie " +
			"that is not expecting a *reply*.")
	}

	select {
	case reply := <-c.replyChan:
		return reply, nil
	case <-c.pingChan:
		return nil, nil
	}
}