1. Download Notepad++. It's free, and you should always have it. It allows you to write code. Not as good as other IDEs but it does the trick for this, and it's very light.

2. Go to your game's folder. Find Package.json. Right Click on it and select "Edit with Notepad++"

3. First line should be like this: "name": "",

Simply click between the last quotes and write the name of your game. For example:

"name": "game-name",

4. Save the file, close any running instances, and launch it again. It's now fixed!

Solution given by "sovok_x" on reddit, I thought I'd share here too cause I had this problem for ages and had no idea how to fix it.

Supposedly, you have to update the NW.js, but I have no idea how to do that either, as no prompts are given to do so in the engine.