HarmonyOS 鸿蒙Next 嵌套数据方法，报错The get method cannot be bound

HarmonyOS 鸿蒙Next 嵌套数据方法，报错The get method cannot be bound 在使用嵌套数据结构时，会报The get method cannot be bound。对于嵌套数据结构要怎么解决？

样例代码片段：

class A {
  ...
  public b: B
}

class B {
  ...
  public item1: HashMap<string, string> = new HashMap<string, string>();
}

@Entry
@Component
struct PoetryPage {
  build{
    ...
    ReaderPage({content: this.PageContent})
  }

  aboutToAppear(): void {
    ...
    this.PageContent=initClassA();
  }
}

@Component
struct ReaderPage {
  @Prop content: A | undefined = undefined;

  build() {
    RelativeContainer() {
      Text(this.content?.b?.item1.get(key))
    }
  }
}