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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _record_from_json(value, field):
 """Coerce 'value' to a mapping, if set or not nullable."""

    if _not_null(value, field):
        record = {}
        record_iter = zip(field.fields, value["f"])
        for subfield, cell in record_iter:
            converter = _CELLDATA_FROM_JSON[subfield.field_type]
            if subfield.mode == "REPEATED":
                value = [converter(item["v"], subfield) for item in cell["v"]]
            else:
                value = converter(cell["v"], subfield)
            record[subfield.name] = value
        return record