Copy doesn't work when model contains cyclic refs

[jri]

On drop when copy is "on" a TypeError is thrown in case the source model contains cyclic references. (My model is a tree structure where the nodes have a "parent" reference.)

When vue-dragula builds the target model for the drop-model event it clones the source model by executing:

JSON.parse(JSON.stringify(sourceModel[dragIndex]))

The TypeError is thrown by JSON.stringify. By default JSON.stringify does not support cyclic references.

A solution would be if vue-dragula would offer an option to let the user configure the "replacer function" (resp. the whitelist array) to be passed as the 2nd argument to JSON.stringify.
https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify

This way the user would get an opportunity to strip the problematic (= cyclic) model properties for stringification.

I'm using Vuejs 2 and vue-dragula 2.0.0-alpha.1 which worked fine until I added the cyclic model reference.