[BUG] TypeError: Cannot set property 'key' of undefined (CheckMatrix)

[Aslihan (Ashley) Saylik]

Environment

Hosting type: Local deployment

npm: 6.11.3

Global packages:
@angular/cli@8.3.10
angular-formio: 4.2.8

OS:
Windows 10

Steps to Reproduce

1. git clone [e-mail]:formio/angular-demo.git
2. npm install -g @angular/cli
3. npm install
4. Implemented #9 solution to the project

Expected behavior

Successful compilation

Observed behavior

I tried to implement "Checkmatrix" component into the form-builder. Form-builder didn't appear and I got this error message. (Seen below)

Form-builder part

I defined the form-builder like this:

<form-builder [options]= '{
  "builder": {
    "basic": false,
    "advanced": false,
    "data": false,
    "layout": false,  
    "customBasic": {      
      "title": "Basic Components",
      "weight": 0,
      "default": false,      
      "components": {  
        "checkmatrix": true
      }
    }    
}}'
[form]="form" class="formio" (change)="onChange($event)"></form-builder>