title: discord.py rewrite | Making errors for my commands
body: <p>Now that I finished my moderation commands [mostly], I am trying to add errors in. I already made the "please specify a member" error, but I cannot manage to make the bot say "this member does not exist" when an invalid name is input.</p>
  
  <pre><code>@client.command(name='kick',
              brief='Kicks user',
              aliases=['Kick'],
              pass_context=True)
  async def kick(context, member:discord.Member=None):
  # Errors
  if not member:
      await context.send('Please specify a member.')
      return
  # Actual Kicking
  if context.author.guild_permissions.kick_members == True:
      await member.kick()
      await context.send(f"{member.mention} was kicked ")
  else:
      await context.send(context.message.author.mention + ", you don't have permission")
  </code></pre>
  
  <p>This is one of my commands, where everything is working. I would like an error which says "User not found" if the member, obviously, doesn't exist. For example, <code>k!kick ijhguiserb</code> would make the bot say, "Member not found," rather than giving me an error in the shell.</p>
  
  <p>Help would be appreciated, thanks!</p>