Error when run the example

[baotnq]

I tried to run the example https://github.com/formio/aurelia-formio/tree/master/example

• npm install to install

• au run --watch to run

• but when drag and drop the element, it not work, with error

TypeError: Cannot read property 'map' of undefined
    at Webform.renderComponents (NestedComponent.js?e8fd:257)
    at Webform.render (Webform.js?ede4:668)
    at WebformBuilder.editComponent (WebformBuilder.js?7ff3:457)
    at WebformBuilder.onDrop (WebformBuilder.js?7ff3:372)
    at Object.eval (WebformBuilder.js?7ff3:308)
    at emitter (emitter.js?f3f2:47)
    at Array.forEach (<anonymous>)
    at Object.eval (emitter.js?f3f2:46)
    at Object.thing.emit (emitter.js?f3f2:38)
    at drop (dragula.js?612e:261)
    at HTMLHtmlElement.release (dragula.js?612e:245)

Please help. Thank you very much