Discord.js --- TypeError：无法读取未定义的属性“ execute”

Question

我正在用Java编写乱码机器人，对于其中一个命令（！server，显示服务器名称和成员总数），错误不断弹出。我当前的代码是;

const fs = require('fs');
client.commands = new Discord.Collection();
const commandFiles = fs.readdirSync('./commands/').filter(file => file.endsWith('.js'));
for(const file of commandFiles){
    const command = require(`./commands/${file}`);
    client.commands.set(command.name, command);
}

client.on('message', message =>{;
    if(message.author.bot) return;
    if (message.content.startsWith("!")){
        const prefix = ("!")
        const args = message.content.slice(prefix.length).split(/ +/);
        const command = args.shift().toLowerCase();
        if(command == 'help'){
            client.commands.get('!help').execute(message, args);
        } 
        if(command == 'server'){
            client.commands.get('!server').execute(message, args);
        } 
        if(command == 'blacklist'){
            client.commands.get('!blacklist').execute(message, args);
        } 
        if(command == 'safe'){
            client.commands.get('!safe').execute(message, args);
        }
    };

错误消息是

            client.commands.get('!server').execute(message, args);
                                          ^

TypeError: Cannot read property 'execute' of undefined

// !server.js File
const Discord = require('discord.js');
const client = new Discord.Client();
module.exports = {
    name: '!server',
    description: "!server",
    execute(message, args){
        message.react('?')
        const serverEmbed = new Discord.MessageEmbed()
        serverEmbed.setTitle(`Server Stats`)
        serverEmbed.addField("Server Name", message.guild.name);
        serverEmbed.addField("Total Members", message.guild.memberCount);
        serverEmbed.addField("Online Members", message.guild.members.cache.filter(member => member.presence.status !== "offline").size);
        serverEmbed.addField("Offline Members", message.guild.members.cache.filter(member => member.presence.status == "offline").size);
        message.channel.send(serverEmbed);
    }
}

该代码适用于其他3个命令！有帮助吗？