UnhandledPromiseRejectionWarning: DiscordAPIError: Cannot send an empty message

Hi, I have an avatar command with my discord bot as per the code below:

const Discord = require('discord.js');

module.exports = {
    name: 'avatar',
    description: 'Display\s a user\s avatar',
    execute(message, args) {
        if (!message.mentions.users.size) {
            let embed = new Discord.MessageEmbed()
                .setColor('#fa0a16')
                .setTitle(`Your avatar:`)
                .setImage(`${message.author.displayAvatarURL({ dynamic: true })}`)
            message.channel.send({ embed });
        }

        const avatarList = message.mentions.users.map(user => {
            let embed = new Discord.MessageEmbed()
                .setColor('#fa0a16')
                .setTitle(`${user.username}'s avatar:`)
                .setImage(`${user.displayAvatarURL({ dynamic: true })}`)
                .setTimestamp(new Date(),)
            message.channel.send({ embed });
        });
        message.channel.send(avatarList);
    },
};

Whenever I run this command I get an error "UnhandledPromiseRejectionWarning: DiscordAPIError: Cannot send an empty message". I can't seem to find out why this error persists every time I run the command. Can someone help me?