[bug] MultiDragPlugin used in a nested Sortables example, when dragging will throw error

[liulinboyi]

Describe the bug

To Reproduce
Steps to reproduce the behavior:
In Macos use MultiDragPlugin in a nested Sortables example, when dragging will throw error

0113.webm

Expected behavior

In Macos use MultiDragPlugin in a nested Sortables example, when dragging don't throw error

Information

Versions - Look in your package.json for this information:
sortablejs = 1.15.6
@types/sortablejs = 1.15.6

Reproduction
jsbin: https://jsbin.com/yacucozupa/1/edit?html,js,output