Object is possibly undefined after undefined check on readonly property

TypeScript Version: 3.7.4, 3.9.2

Search Terms:
Object is possibly undefined
undefined readonly callback
Code

class Test {
  private readonly testProperty?: { value: number };
  public constructor(testProperty: { value: number }) {
    this.testProperty = testProperty;
  }

  public method() {
    if (this.testProperty) {
      Promise.resolve().then(() => this.testProperty.value); //Object is possibly undefined
    }
  }
}

Expected behavior:
testProperty should not be resolved as possibly undefined as this is not possible in this scenario as the property has already been checked and it is marked as readonly.

Actual behavior:
testProperty is possibly undefined, requiring another undefined check.

Playground Link:
https://www.typescriptlang.org/play/#code/MYGwhgzhAEAqCmEAu0DeAoa0AOAnAlgG5hLzS7xgAmA9gHYgCe0pyACrjdvLkowPwAuNNGIgArvGF1xAWwBGPaAF8A3Jhzj5IfMGjB6yXOOBIauABSskHLjz7DUosBKnQZCpcoCUaDViQAC3wIADprW25eZgBeFkQbTii+dSxldA1sLR09WXggmioLXwwsLHwAM2grYLCIpPtGEv8y21kQ+FCKCBoQQnhi8MD4Ogti6BiAPhZa8ITIxtCxSW9VaAB6dYB5eQAreFNoEJwaKHxtZnE6KngK-Dp4Khb0tPRlIA

Related Issues:

Similar issues but these i understand why TypeScript would report an error, in my case the property is readonly so it seems like a bug to me.
https://github.com/microsoft/TypeScript/issues/38053
https://github.com/microsoft/TypeScript/issues/11498

从链接的 Playground 复现开始，并比较相关 issue #38053 和 #11498 中描述的行为。跟踪 Promise 回调内部 readonly optional property 的类型检查；当所提供的示例不再报告“possibly undefined”，或预期行为以其他方式得到解决时，即视为完成。