serverTimestamps with estimate returns null

[mnlfischer]

Hello Community,

I use the following code in my react app to get docs from firestore.

    const unsubscribe = onSnapshot(q, (querySnapshot) => {
      const data = querySnapshot.docs.map((doc) => {
        const transformedData = doc.data({ serverTimestamps: 'estimate' });
        console.log(transformedData);
    });

I expected that the createdAt prop in the doc returns an estimated value but I got null.
createdAt is created with serverTimestamp().

Do I something wrong?

I use 9...-beta.6