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.

{
    "stammdaten.datensatz_erzeuger": [{
        "id": 1000,
        "bezeichnung": "Testbezeichnung",
        "netzbetreiber_id": "06",
        "mst_id": "06010",
        "datensatz_erzeuger_id": "06"
    }]
}