title: .joinedAt proprety always returning undefined in discord.js
body: <p>im trying to make a userinfo command right now on my discord bot. one of the fields is the time that the user joined the server. </p>
  
  <p>heres my code </p>
  
  <pre><code>module.exports.run = async (Client, msg, args, UserDataBase, messages, commands_ran) =&gt; {
      let user = msg.guild.member(msg.mentions.users.first() || msg.guild.members.get(args[0]))
  
      if(!user) {
          user = msg.author
      }else {
           user = user.user
      }
  
      const embed = new Discord.RichEmbed()
      .setTitle('**User info**')
      .setThumbnail(user.avatarURL)
      .addField('Name:', user.username,true)
      .addField('Tag:', `#${user.discriminator}`,true)
      .addField('Date Joined:', user.createdAt)
      .addField('Joined Server:', user.joinedAt)
      msg.channel.send(embed)
  }
  </code></pre>
  
  <p>it always returns Undefined in the <a href="https://drizzy.is-terrible.com/EYEI72" rel="nofollow noreferrer">final product</a></p>