请教下节点是个什么概念呢，为什么本地 mac 环境搭建好，创建节点报错呢

TypeError: Cannot read property 'length' of null AdminNode.getIndexFromNodeId src/github.com/casbin/casbin-forum/web/src/admin/AdminNode.js:213 210 | } 211 | 212 | getIndexFromNodeId (nodeId) {

213 | for (let i = 0; i <this.state.nodes.length; i++) { | ^ 214 | if (this.state.nodes i.nodeInfo.id === nodeId) { 215 | return i; 216 | } View compiled AdminNode.renderSelect src/github.com/casbin/casbin-forum/web/src/admin/AdminNode.js:447 444 | let value, data; 445 | switch (item) { 446 | case "node": 447 | value = this.getIndexFromNodeId (this.state.form.parentNode); | ^ 448 | data= this.state.nodes.map ((node, i) => { 449 | return {text: ${node.nodeInfo.name} / ${node.nodeInfo.id}, id: i}; 450 | }); View compiled AdminNode.render src/github.com/casbin/casbin-forum/web/src/admin/AdminNode.js:688 685 | 686 | 687 | {i18next.t ("node:Parent node")} 688 | | ^ 689 | {this.renderSelect ("node")} 690 | 691 |