我正在try 制作一个discord机器人，但标题中出现了错误.这是我的代码:

import discord
import os
from dotenv import load_dotenv
from discord.ext import commands
import logging


class DiscordBot:
    def __init__(self) -> None:
        self.intents = discord.Intents.all()
        self.intents.messages = True
        self.intents.message_content = True
        self.intents.guilds = True
        self.intents.members = True
        self.intents.presences = True
        self.bot = commands.Bot(command_prefix='$', intents=self.intents)

    async def on_ready(self):
        print("Bot is ready.")
    
    @commands.command()
    async def hello(self, ctx):
        await ctx.channel.send('Hello!')
        print("HELLO!")


if __name__ == '__main__':
    load_dotenv()

    TOKEN = os.getenv('DISCORD_TOKEN_KEY')

    logging.basicConfig(level=logging.DEBUG)
    bot = DiscordBot()
    bot.bot.add_command(bot.hello)

    bot.bot.run(TOKEN)

以下是完整的错误追溯:

    ERROR:discord.ext.commands.bot:Ignoring exception in command hello
    Traceback (most recent call last):
      File "/home/dimo/programming/discord-bot/mybot-env/lib/python3.12/site-packages/discord/ext/commands/core.py", line 235, in wrapped
        ret = await coro(*args, **kwargs)
                    ^^^^^^^^^^^^^^^^^^^^^
    TypeError: DiscordBot.hello() missing 1 required positional argument: 'ctx'
    
    The above exception was the direct cause of the following exception:
    
    Traceback (most recent call last):
      File "/home/dimo/programming/discord-bot/mybot-env/lib/python3.12/site-packages/discord/ext/commands/bot.py", line 1350, in invoke
        await ctx.command.invoke(ctx)
      File "/home/dimo/programming/discord-bot/mybot-env/lib/python3.12/site-packages/discord/ext/commands/core.py", line 1029, in invoke
        await injected(*ctx.args, **ctx.kwargs)  # type: ignore
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/home/dimo/programming/discord-bot/mybot-env/lib/python3.12/site-packages/discord/ext/commands/core.py", line 244, in wrapped
        raise CommandInvokeError(exc) from exc
    discord.ext.commands.errors.CommandInvokeError: Command raised an exception: TypeError: DiscordBot.hello() missing 1 required positional argument: 'ctx'

为什么会发生这种情况？如何解决它？