Update Record with added item in nested array

I have the following on-device data source schema for users (I also have the same structure as app variable):

    "id": "6237ea82-854e-4242-a8db-21632c23d143",
    "userName": "johndoe",
    "userJournals": [
            "id": "6237ea82-854e-4242-a8db-21632c23d143",
            "journalText": "Lorem ipsum dolor sit amet",
            "journalTitle": "Lorem ipsum"

I’d like to add a new item every time user creates a journal.

  1. I set a page variable (newJournal) which is the object for journal (containing exact same fields)
  2. I use WITH_ITEM(appVars.userVariable.userJournals, pageVars.newJournal)
  3. I update my user record with the app variable.

When I checked the debugger I saw that my after I use “set app variable” it actually sets it as “null”.

Where am I doing wrong?