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

Beginne mit der verknüpften Playground-Reproduktion und vergleiche das in den verwandten Issues #38053 und #11498 beschriebene Verhalten. Verfolge die Typprüfung für die readonly optional property innerhalb des Promise-Callbacks; abgeschlossen ist die Arbeit, wenn das bereitgestellte Beispiel nicht mehr „possibly undefined“ meldet oder das erwartete Verhalten anderweitig behoben ist.