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

リンクされている Playground の再現例から始め、関連する issue #38053 と #11498 に記載された挙動を比較してください。Promise コールバック内の readonly optional property に対する型チェックを追跡してください。完了の条件は、提示された例で「possibly undefined」が報告されなくなるか、期待される挙動が別の形で解決されることです。