CascadeSelect onGroupChange returns undefined

[leitgebmartin]

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Plunkr Case (Bug Reports)
https://stackblitz.com/edit/github-dbxv7q?file=src%2Fapp%2Fapp.component.ts

Current behavior
The event submitted to the callback function of onGroupChange is always undefined.

Expected behavior
As described in the documentation, it should be:
event.originalEvent: Original event
event.value: Selected option group

• Angular version:
  11.2.X

• PrimeNG version:
  11.3.0

• Browser:
  Chrome 89