When deleting all nutrients, some computed values are kept in DB

[raphael0202]

When we remove all nutrients from a product using the web version, we still have the following (computed values) in the nutriments field:

{
    "nutriments": {
        "carbon-footprint-from-known-ingredients_100g": 50.336,
        "carbon-footprint-from-known-ingredients_product": 252,
        "carbon-footprint-from-known-ingredients_serving": 27.2,
        "fruits-vegetables-legumes-estimate-from-ingredients_100g": 0,
        "fruits-vegetables-legumes-estimate-from-ingredients_serving": 0,
        "fruits-vegetables-nuts-estimate-from-ingredients_100g": 0,
        "fruits-vegetables-nuts-estimate-from-ingredients_serving": 0,
        "nova-group": 1,
        "nova-group_100g": 1,
        "nova-group_serving": 1,
        "nutrition-score-fr": -7,
        "nutrition-score-fr_100g": -7
    }
}

In Robotoff, I added a special case to consider the product nutrients as missing if there are only these keys: openfoodfacts/robotoff@0e4aff3.

[stephanegigandet]

@raphael0202 We chose to have some computed values in the nutriments field, so this behaviour is normal. It is useful in particular for easing the creation of graphs and search filters. We could decide to do it differently in the future.