HarmonyOS AppStorage将某个字段设置为null，无法被观测

AppStorage.setOrCreate('PropA', 47)  
@Entry()  
@Component  
struct CompA {  
  @Watch('test') @StorageLink('PropA') storageLink: number | null = 1;  
  test() {  
    console.log('storageLink' + AppStorage.get('PropA'))  
  }  
  build() {  
    Column({ space: 20 }) {  
      Text(`From AppStorage ${this.storageLink}`)  
        .onClick(() => {  
          if (this.storageLink) {  
            this.storageLink++  
          }  
        })  
      Button('delete').onClick(() => {  
        this.storageLink = null  
      })  
    }  
  }  
}