Java、Discord4Jを用いたBotでのメッセージ送信

Question

前提・実現したいこと

Discord4Jを使ってBotを作成し、特定の発言に対してbotが返答を行うだけの簡単なプログラムを書いています。

メッセージを返信する機能を実装中に以下のエラーメッセージが発生しました。

発生している問題・エラーメッセージ

Message could not be sent with error: 
sx.blah.discord.util.DiscordException: Attempt to send message before shard is ready!
	at sx.blah.discord.api.IShard.checkReady(IShard.java:73)
	at sx.blah.discord.handle.impl.obj.Channel.sendMessage(Channel.java:459)
	at sx.blah.discord.handle.impl.obj.Channel.sendMessage(Channel.java:449)
	at sx.blah.discord.handle.impl.obj.Channel.sendMessage(Channel.java:439)
	at main.com.ensemblebox.iberisbot.BotUtils.lambda$sendMessage$0(BotUtils.java:30)
	at sx.blah.discord.util.RequestBuffer.lambda$request$1(RequestBuffer.java:84)
	at sx.blah.discord.util.RequestBuffer$RequestFuture$RequestCallable.call(RequestBuffer.java:286)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
	at sx.blah.discord.util.RequestBuffer$RequestFuture.run(RequestBuffer.java:259)
	at sx.blah.discord.util.RequestBuffer$RequestFuture.access$200(RequestBuffer.java:162)
	at sx.blah.discord.util.RequestBuffer.lambda$request$0(RequestBuffer.java:50)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1135)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
	at java.base/java.lang.Thread.run(Thread.java:844)

該当のソースコード

/*Main.java*/
package main.com.marumaru.bot;

import sx.blah.discord.api.IDiscordClient;

public class Main {

    public static void main(String[] args) {

        if(args.length != 1){
            System.out.println("Please enter the bots token as the first argument e.g java -jar thisjar.jar tokenhere");
            return;
        }

        IDiscordClient client = BotUtils.getBuiltDiscordClient(args[0]);

        /*
        // Commented out as you don't really want duplicate listeners unless you're intentionally writing your code
        // like that.
        // Register a listener via the IListener interface
        cli.getDispatcher().registerListener(new IListener<MessageReceivedEvent>() {
            public void handle(MessageReceivedEvent event) {
                if(event.getMessage().getContent().startsWith(BotUtils.BOT_PREFIX + "test"))
                    BotUtils.sendMessage(event.getChannel(), "I am sending a message from an IListener listener");
            }
        });
        */

        // Register a listener via the EventSubscriber annotation which allows for organisation and delegation of events
        client.getDispatcher().registerListener(new MyEvents());

        // Only login after all events are registered otherwise some may be missed.
        client.login();
    }

}

/*BotUtils.java*/
package main.com.marumaru.bot;

import sx.blah.discord.api.ClientBuilder;
import sx.blah.discord.api.IDiscordClient;
import sx.blah.discord.handle.obj.IChannel;
import sx.blah.discord.util.DiscordException;
import sx.blah.discord.util.RequestBuffer;

class BotUtils {

    // Constants for use throughout the bot
    static String BOT_PREFIX = "i!";

    // Handles the creation and getting of a IDiscordClient object for a token
    static IDiscordClient getBuiltDiscordClient(String token) {

        // The ClientBuilder object is where you will attach your params for configuring the instance of your bot.
        // Such as withToken, setDaemon etc
        return new ClientBuilder()
                .withToken(token)
                .build();

    }

    // Helper functions to make certain aspects of the bot easier to use.
    static void sendMessage(IChannel channel, String message){
        // This might look weird but it'll be explained in another page.
        RequestBuffer.request(() -> {
            try{
                channel.sendMessage(message);/* 問題の30行目 */
            } catch (DiscordException e){
                System.err.println("Message could not be sent with error: ");
                e.printStackTrace();
            }
        });

        /*
        // The below example is written to demonstrate sending a message if you want to catch the RLE for logging purposes
        RequestBuffer.request(() -> {
            try{
                channel.sendMessage(message);
            } catch (RateLimitException e){
                System.out.println("Do some logging");
                throw e;
            }
        });
        */

    }
}

/* MyEvents.java*/
package main.com.marumaru.bot;

import sx.blah.discord.api.events.EventSubscriber;
import sx.blah.discord.handle.impl.events.ReadyEvent;
import sx.blah.discord.handle.impl.events.guild.channel.message.MessageReceivedEvent;

public class MyEvents {

    @EventSubscriber
    public void onReady(ReadyEvent event) {
        System.out.println("Bot is Stand by ready.");
    }

    @EventSubscriber
    public void onMessageReceived(MessageReceivedEvent event) {
        System.out.println(event.getMessage().getContent());
        if(event.getMessage().getContent().startsWith(BotUtils.BOT_PREFIX + "test"))
            BotUtils.sendMessage(event.getChannel(), "I am sending a message from an EventSubscriber listener");
    }

}

試したこと

Readyする前にメッセージの送信を行っているからエラーを吐いているのだと思いますが…

参照したQiitaの記事ではログインが完了するとReadyEventsが実行されるとありましたので、client.isLoggedIn()やclient.isReady()などで状態を確認しましたが、ログインはtrueが帰るのに対し、isReadyはfalseを返し続けてしまい。良く分かっていない状態です…

何卒みなさんのお力をお貸ししていただけないでしょうか…?

補足情報（FW/ツールのバージョンなど）

Intellij IDEA
JavaSE10
ソースコード自体はこれと全く同じです。
https://discord4j.readthedocs.io/en/latest/Basic-bot/