As soon as I import the tree component into my project's component (nothing more is required) it complains with the error described in the title. I use following versions: vue-draggable-nested-tree: "^2.2.18", tree-helper: "^1.4.14", draggable-helper: "^3.0.4", node: v12.14.0 yarn: 1.10.1 ```vue <script> import Layout from '../../../components/Layout.vue' import {DraggableTree} from 'vue-draggable-nested-tree' // import {forIn} from 'tree-helper' // import _ from 'underscore' export default { name: 'MenuItemsEditPage', components: { Layout, Tree: DraggableTree }, ... ```