DragEvent not passed to pull() if target is empty

[JivanRoquet]

A series of sortable containers is created, each with the following constructor options:

{
 group: {
  name: 'drag',
  pull(to, from, element, e) {
    console.log(e) // this is where we can see the difference in behaviour
  }
}

In the pull() callback above, we console.log(e) to show the event that was passed to the callback.

When dragging an element from one container to a different container which already has at least one element in it, the object being logged is of the following form:

DragEvent {isTrusted: true, dataTransfer: DataTransfer, screenX: 530, screenY: 297, clientX: 530, …}

And when dragging an element from one container to a different container which is currently empty, the object being logged is of the following form:

{clientX: 496, clientY: 213, target: div.col-items-content, rootEl: div.col-items-content}

The context of this issue is I want to tie a e.ctrlKey if-check to return a different value from the pull() callback, like the following:

pull(to, from, element, e) {
  if (e.ctrlKey) {
    return 'clone'
  } else {
    return true
  }
}

This works great when pulling an element onto an already-filled container, but unfortunately, because of the behaviour described above, this doesn't work when pulling an element into a container which is so far still empty.

JSFiddle of the reproduction: https://jsfiddle.net/xc6hLy17/4/

In this JSFiddle, play with the elements, try to empty a container and fill it again, and check that a DragEvent is correctly fired when dragging an item onto a non-empty ul container, but not when dragging an item onto an empty container.

[owen-m1]

Solved in b483211.