[cloud_firestore] I want to add new field to the document at the new version of my application

[KeepUpCode]

I want to add new field to the document at the new version of my application. But my last version of the application database didn't have this field.
For example, In the users collection, each user document have name ande email.

{
  "users": {
    "uid1": {
      "name": "Lily",
      "email": "[email protected]"
    },
    "uid2": { ... },
    "uid3": { ... }
  }
}

In the new version of application, i need new field phoneNumber. But when I read the data I got an error : Bad state: field does not exist within the DocumentSnapshotPlatform

documentSnapshot.get('phoneNumber')

if there is a way to check if a property is present in a Cloud Firestore document. Something like document.contains("phoneNumber") or if there is a document property exist.

Or should I run a code to add fields in the old db?

What would be the best practice to include in all the existing documents of the DB without losing their data on a new version of the app? Should I run an snippet just once to do this task or are there any better approaches to the problem?