title: error message for missing argument, discord.py
body: <p>I'm very new to coding and am currently working on a discord bot, I would like to make it so that If the kick command is missing the member arg the bot will reply with 'user not found.' The code below is currently in a cog.</p>
  <pre><code>@commands.command()
  @commands.has_permissions(kick_members=True)
  async def kick(self, ctx, member: discord.Member, *, reason=None):
      await member.kick(reason=reason)
      await ctx.send(f'user {member} was kicked reason: &quot;{reason}&quot;')
  </code></pre>