Cannot read property username of undefinded discord.js - node.js

Question

I am making a ship command, the error messages work but the shipping does not. I always get this error: Type Error: Cannot read property "username" of undefined. Can someone help me to fix it?
Here is my code:
const { DiscordAPIError } = require("discord.js");
const Discord = require('discord.js');
const client = new Discord.Client();
module.exports = {
name: 'ship',
description: "Ship two users!",
execute(message, args) {
const user = message.mentions.members.first();
const user2 = message.mentions.members.first(+1) ;
const images = [(1-100) code is different, put every number there]
const result = Math.floor(Math.random() * images.length);
const error = new Discord.MessageEmbed()
.setColor("#000000")
.setTitle("Ship")
.setDescription("There was an error: Check if you mentioned a user other than you!")
.setFooter(message.author.username)
.setTimestamp()
;
if(!user) return message.reply(error);
if(!user2) user2 = message.author.username;
if(user.id === message.author.id) return message.reply(error);
const embed = new Discord.MessageEmbed()
.setColor("#2A333E")
.setTitle("Ship")
.setDescription(user2.user.username + " + " + user.user.username + " =")
.addField(images[result] + "%" , "Is this good or not so good?")
.setFooter(message.author.username)
.setTimestamp()
;
message.channel.send(embed)
}}

Answer 1

if(!user2) user2 = message.author.username;
This is the problematic line - you're setting the value of user2 to equal the author's username. Try setting it to equal just message.author instead.
Additionally, you're trying to retrieve the .user property from User objects, which does not exist (since it's already a User object.) You'll need to change user2.user.username and user.user.username to just user2.username and user.username