Error while generating getter function for selector

[btnevan]

I am getting this error in my console:

Error while generating getter function for selector : portal.fields.fields.fieldId NOTE: Define manually

I need to find a way to use that data, but do not know how to "define manually" as suggested by the error.

The JSON is presented in the following format (I have no way of changing this nesting)

{
    "items": [
        {
            "id": 123456,
            "portal": {
                "fields": [
                    {
                        "fieldId": 100001,
                        "fieldName": "CategoryA",
                        "valueId": 123456,
                        "value": "ValueX",
                        "fields": [
                            {
                                "fieldId": 200001,
                                "fieldName": "SubCategoryA",
                                "valueId": 123459,
                                "value": "SubValueA"
                            }
                        ]
                    },
                    {
                        "fieldId": 100002,
                        "fieldName": "CategoryB",
                        "valueId": 123457,
                        "value": "ValueY"
                    },
                    {
                        "fieldId": 100003,
                        "fieldName": "CategoryC",
                        "valueId": 123458,
                        "value": "ValueZ"
                    }
                ]
            },
            "date": "2019-02-11"
        }
    ],
    "totalCount": 1
}   

I simply need to display the value of each object (in this example, ValueX, ValueY, ValueZ, and SubValueA) . The other keys-value pairs of fieldId, fieldName, and valueId are not important for my implementation.

Can you please provide some assistance.