QUESTION : How to create new custom manager?

During this time, I tried to add my custom manager to grapesjs on npm.

// editor/index.js
        ['Styles', 'StyleManager'],
        'DeviceManager',
        ['Devices', 'DeviceManager'],
        'PackageManager', //this
      ].forEach(prop => {
        if (Array.isArray(prop)) {
          this[prop[0]] = em.get(prop[1]);

and

//editor/model/Editor.js

const deps = [
...
  require('block_manager'),
  require('package_manager'), // this
];

However, I failed.

This is my test code:

export default () =>{
    return {
        name : "PackageManager",

        test(){
            console.log("hello form package manager");
        }
    }
}

When I build, I am taking a blank page. Please rescue me from this black hole.

Thanks.