ChangeEvent Trigger updateDescription undefined

Hello All,

Trying to figure out how can I update(or replace) embedded documents of other users documents (members part of a project), and with mu current schema as User document contain the embedded object, I call a trigger on it.
My issue is that in function the chageEvent brings undefined on updatedDescription (where I should see the changed field/value), any idea why ?

exports = function(changeEvent) {
  const { updateDescription, fullDocument } = changeEvent;
  const db ="mongodb-atlas").db("myDB);
  console.log(`Update happen on ${JSON.stringify(updateDescription)}`);

Maybe important to mention that the change is done on an ObservableRealmObject in swift app.