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: wx_CloseOrder.go
    path of file: ./repos/gopay/examples/wechat
    
    the code of the file until where you have to start completion: package wechat

import (
	"github.com/go-pay/gopay"
	"github.com/go-pay/gopay/wechat"
	"github.com/go-pay/util"
	"github.com/go-pay/xlog"
)

func CloseOrder() {
	// client只需要初始化一个，此处为了演示，每个方法都做了初始化
	// 初始化微信客户端
	//    appId：应用ID
	//    MchID：商户ID
	//    A
    
func CloseOrder() {
	// client只需要初始化一个，此处为了演示，每个方法都做了初始化
	// 初始化微信客户端
	//    appId：应用ID
	//    MchID：商户ID
	//    ApiKey：Key值
	//    isProd：是否是正式环境
	client := wechat.NewClient("wxdaa2ab9ef87b5497", "1368139502", "GFDS8j98rewnmgl45wHTt980jg543abc", false)

	// 初始化参数结构体
	bm := make(gopay.BodyMap)
	bm.Set("out_trade_no", "MfZC2segKxh0bnJSELbvKNeH3d9oWvvQ").
		Set("nonce_str", util.RandomString(32)).
		Set("sign_type", wechat.SignType_MD5)

	// 请求关闭订单，成功后得到结果
	wxRsp, err := client.CloseOrder(ctx, bm)
	if err != nil {
		xlog.Error(err)
		return
	}
	xlog.Debug("Response：", wxRsp)
}