[p-tree] event.accept() not available on first drop

[leifjones]

Thank you for the fix of #9991 with the release of 11.3.2. However, we're blocked by a related issue:

Even though, the event is now triggered. The first fire of the event doesn't have an accept() method. Thus our current implementation's attempt to utilize that method throws an error.

I'm submitting a ... (check one with "x")

[x] bug report => Search github for a similar issue or PR before submitting
[ ] feature request => Please check if request is not on the roadmap already https://github.com/primefaces/primeng/wiki/Roadmap
[ ] support request => Please do not submit support request here, instead see http://forum.primefaces.org/viewforum.php?f=35

Plunkr Case (Bug Reports)
https://stackblitz.com/edit/primeng-treedragdrop-demo-4bbf54?file=src%2Fapp%2Fapp.component.ts

Current behavior

1. The accept() method is not present the first time we drop the item. (It is there the second time we drop the item.)
2. Apparently event.accept() does get called on/before/after this first drop to an empty list (Evidence: nodes get removed from source and added to target) event though it's not triggered by/accessible to the onDrop function.

Expected behavior

1. The event.accept() is present on the event on the first drop.
2. If the user onDrop method we provide, doesn't call the event.accept() method, the dropped node does not leave the source and get added to the target.

Minimal reproduction of the problem with instructions

See stackblitz and gif above

What is the motivation / use case for changing the behavior?

We need to:
a. validate the note and NOT accept() if criteria aren't met
b. copy and restore the dragged item in the source list before accept()
c. change the type of the dropped node

onDrop(event) {
  try {
    //
    const tentativeParent = // custom logic utilizing event.dragNode, event.dropNode

    // validation
    if (failureCondition) {
      // tell user
      return; // don't accept()
    }

    // copy and restore in source
    const copy: MyClass = new MyClass(event.dragNode);
    this.listOfSourceNodes.push(copy);
    this.listOfSourceNodes.sort((a, b) => this.mySourceNodeSorter(a, b));

    // approve drop
    event.accept();

    // transform
    event.dragNode.parentMyValue = tentativeParent.myValue;
    event.dragNode.draggable = true;
    event.dragNode.type = 'myTemplateString';
    tentativeParent.expanded = true;
  } catch (error) {
    // Report error
  }
}

Please tell us about your environment:

Windows 10, Visual Studio Code, NPM 7.9

• Angular version: 11.2.9

• PrimeNG version: 11.3.2

• Browser: Only tried on Chrome 89

• Language: TypeScript 4.0.5

• Node (for AoT issues): node --version = 14.15.3

[yigitfindikli]

Fixed in 4a275dd