create table json_test (
    my_data jsonb);

{"details": [
    {
        "f1": "",
        "f2": "free text"
    },
    {
        "f1": "",
        "f2": "free text"
    }
]}

{"details": [
    {
        **"f1": null,**
        "f2": "free text"
    },
    {
        **"f1": null,**
        "f2": "free text"
    }
]}