Ninja: select json values with `shownull=true` gives duplicates, distinguish between JSON null and non-existent

[Piiit]

We have a duplicate with "smetadata.state": null.
One is about an existing JSON field inside smetadata, with a JSON null value, the other is a JSON object without a state key.

http://tomcat.testingmachine.eu/ninja/api/v2/flat/EChargingStation?shownull=true&select=smetadata.state
gives

{
    "offset": 0,
    "data": [
        {
            "smetadata.state": null
        },
        {
            "smetadata.state": "TEMPORARYUNAVAILABLE"
        },
        {
            "smetadata.state": "UNKNOWN"
        },
        {
            "smetadata.state": "UNAVAILABLE"
        },
        {
            "smetadata.state": "AVAILABLE"
        },
        {
            "smetadata.state": "FAULT"
        },
        {
            "smetadata.state": "ACTIVE"
        },
        {
            "smetadata.state": "OCCUPIED"
        },
        {
            "smetadata.state": null
        },
        {
            "smetadata.state": "MAINTENANCE"
        }
    ],
    "limit": 200
}

[sseppi]

@clezag Is this issue still of interest, shall we keep it or discuss it during one of the next strategy meetings?

[clezag]

@sseppi removed from project, currently not planned.