title: Discord Bot cant leave voice channel 'NoneType' object has no attribute 'disconnect'
body: <p>So I started working on a music bot and I keep getting this when I try to leave. Joining a voice channel works fine.</p>
  
  <pre><code>discord.ext.commands.errors.CommandInvokeError: Command raised an exception: AttributeError: 'NoneType' object has no attribute 'disconnect'
  </code></pre>
  
  <p>And my code is </p>
  
  <pre><code>@client.command(name = "join",
                  pass_context = True)
  async def join(ctx):
      channel = ctx.message.author.voice.voice_channel
      await client.join_voice_channel(channel)
      print("Bot joined the voice channel")
  
  @client.command(name = "leave",
                  pass_context = True)
  async def leave(ctx):
      server = ctx.message.server
      voice_client = client.voice_client_in(server)
      await voice_client.disconnect()
      print("Bot left the voice channel")
  </code></pre>
  
  <p>Also im using the following libraries:</p>
  
  <pre><code>import discord
  from discord.ext.commands import Bot
  from discord.ext import commands
  from discord import Game
  import random
  </code></pre>