報錯 [Vue warn]: Error in directive contextmenu bind hook: "TypeError: Cannot read property '$refs' of undefined"  <div :class="['box', theme]" v-contextmenu:contextmenu>    <Tree :data="data1" @on-select-change="treeChange"></Tree>  </div>  <v-contextmenu :theme="theme" ref="contextmenu">    <v-contextmenu-item>菜單1</v-contextmenu-item>    <v-contextmenu-item>菜單2</v-contextmenu-item>    <v-contextmenu-item>菜單3</v-contextmenu-item>  </v-contextmenu>        import Vue from 'vue'  import contentmenu from 'v-contextmenu'  import 'v-contextmenu/dist/index.css'  import Contextmenu from 'v-contextmenu'  import ContextmenuItem from 'v-contextmenu'  Vue.use(contentmenu)  求別貼源碼地址了。。。我已經翻了很多遍了。。謝謝大佬們。。。