Fix identification of identifier for error report. Setting it to null if the previous attempt was successfull already obviously was a flaw. Using the wrong key HAUPTPROBEN_NR probably could have been avoided by usage of appropriate constants.

{
    "land.messwert": [{
        "id": 1003,
        "messungs_id": 1200,
        "messgroesse_id": 56,
        "messwert": 1.5,
        "meh_id": 207
    }]
}