shouldCopyOnOutsideDrop gets undefined in callback function

Hi, guys.
I use "react-dnd" for copying node from SortableTree to another component.

My issue for react-dnd: https://github.com/react-dnd/react-dnd/issues/1221

I want to use shouldCopyOnOutsideDrop to prevent deleting draggable node from SortableTree, but I receive undefined in callback and error after dropping node:

```
{
console.log('!!shouldCopyOnOutsideDrop node', node);
// {node: undefined, prevTreeIndex: undefined, prevPath: undefined}

return true;
}}
dndType={'myDndType'}
....
>
...

```

```
Uncaught TypeError: Cannot read property 'length' of undefined
```

Please, help me for fix the problem.