HarmonyOS 编译报错If a component attribute supports local initialization, a valid, runtime-independent default value should be set for it

@CustomDialog
struct CustomDialogExample {
  cancel?: () => void
  confirm?: () => void
  controller: CustomDialogController

  build() {
    Column() {
      Text('我是内容').fontSize(20).margin({ top: 10, bottom: 10 })
      Flex({ justifyContent: FlexAlign.SpaceAround }) {
        Button('cancel')
          .onClick(() => {
            this.controller.close()
            if (this.cancel) {
              this.cancel()
            }
          }).backgroundColor(0xffffff).fontColor(Color.Black)
        Button('confirm')
          .onClick(() => {
            this.controller.close()
            if (this.confirm) {
              this.confirm()
            }
          }).backgroundColor(0xffffff).fontColor(Color.Red)
      }.margin({ bottom: 10 })
    }
  }
}

@Entry
@Component
struct CustomDialogUser {
  dialogController: CustomDialogController = new CustomDialogController({
    builder: CustomDialogExample({
      cancel: ()=> { this.onCancel() },
      confirm: ()=> { this.onAccept() },
    }),
  })
  onCancel() {
    console.info('Callback when the first button is clicked')
  }
  onAccept() {
    console.info('Callback when the second button is clicked')
  }
  build() {
    Column() {
      Button('click me')
        .onClick(() => {
          this.dialogController.open()
        })
    }.width('100%').margin({ top: 5 })
  }
}

preview会报错。