I am trying to make a discord.js avatar command, and the mentioning portion doesn't work correctly

Question

I have an avatar command in my discord bot. When the user uses h.avatar, it outputs their avatar, which works fine. Whenever they try to use h.avatar @use

Answer 1

 if (message.content.startsWith(prefix + 'avatar')) {
   let user = message.mentions.users.first();
   if(!user) user = message.author;
   let color = message.member.displayHexColor;
   if (color == '#000000') color = message.member.hoistRole.hexColor;
   const embed = new Discord.RichEmbed()
                   .setImage(user.avatarURL)
                   .setColor(color)
    message.channel.send({embed});
 }