HarmonyOS Object is possibly 'undefined'. <ArkTSCheck>报错

参照以下写法

if (this.port_pair_map != undefined && this.port_pair_map.get("123") != undefined) {
  let arr: webview.WebMessagePort[] = this.port_pair_map.get("123") as webview.WebMessagePort[]
    // arr[1].postMessageEvent("11111")
  (this.port_pair_map.get("123") as webview.WebMessagePort[])[1].postMessageEvent("1111")
}