title: How to use discord.py event handler on_voice_state_update to run only when a user joins a voice channel
body: <p>I am trying to learn how to make a discord bot through <code>discord.py</code> and wanted to add a feature where a message would be sent from the bot whenever another user joined the voice channel that the bot is currently in. I do not know how to use the event handler itself and didn't understand their documentation enough to utilize it. </p>
  
  <pre><code>from discord.ext.commands import Bot 
  client = Bot(command_prefix="!")
  
  @client.event
  async def on_voice_state_update(before, after):
      await client.say("Howdy")
  </code></pre>
  
  <p>From my limited understanding of the documentation, the event handler should be used whenever a user is muted, deafened, leaves, or joins a channel.</p>
  
  <p>However, even when I tried to get it to recognize those actions it gave me an error message of:</p>
  
  <pre><code>Ignoring exception in on_voice_state_update
  Traceback (most recent call last):
    File "C:\Users\Sam\PycharmProjects\FunBotProject\venv\lib\site-packages\discord\client.py", line 307, in _run_event
      yield from getattr(self, event)(*args, **kwargs)
    File "C:/Users/Sam/PycharmProjects/FunBotProject/my_bot2.py", line 63, in on_voice_state_update
      await client.say("Xd ")
    File "C:\Users\Sam\PycharmProjects\FunBotProject\venv\lib\site-packages\discord\ext\commands\bot.py", line 309, in _augmented_msg
      msg = yield from coro
    File "C:\Users\Sam\PycharmProjects\FunBotProject\venv\lib\site-packages\discord\client.py", line 1145, in send_message
      channel_id, guild_id = yield from self._resolve_destination(destination)
    File "C:\Users\Sam\PycharmProjects\FunBotProject\venv\lib\site-packages\discord\client.py", line 289, in _resolve_destination
      raise InvalidArgument(fmt.format(destination))
  discord.errors.InvalidArgument: Destination must be Channel, PrivateChannel, User, or Object. Received NoneType
  </code></pre>