Uncaught TypeError: Cannot read property ‘appendChild’ of undefined. Meaning the dom variable is undefined.

The error points to main.js line 38:

var dom = document.createElement("div");
dom.id = module.identifier;
dom.className = module.name;

if (typeof module.data.classes === "string") {
     dom.className = "module " + dom.className + " " + module.data.classes;
}

dom.opacity = 0;
wrapper.appendChild(dom);

Everything still works fine, including the custom modules I’ve built, which is actually what drove me to the forum. Since everything works, I’m not actually sure how to debug. Wanted to see if anyone else had this problem or maybe had an easy fix for a fellow perfectionist.