Parameters "nitrateConcentration" and "sulfateConcentration" in Irrigation event not optional

[specka]

For the AgMIP calibration study I created json simulation files. In some crop rotations there were irrigation events thatI accordingly configured in the json files. But as I got no information about nitrate and sulfate concentration I left out the parameters section in the irrigation event as it should be optional (according to the Wiki documentation). But when I run the monica simulation, an error in the file 'json11-helper.h' at line 412 was raised.

Error @ Tools::set_value_obj_value: bad type for parameters in {"amount": [27, "
mm"], "date": "2011-04-13", "type": "Irrigation"}
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