def METHOD_NAME(self, values, json_key, value):
    """To manage defaults, you can use a specific resolver."""
    key, sep, marshaller = json_key.partition("=")
    if marshaller == "list":  # sublist field
        if not values.get(key):
            values[key] = []
        values[key].append(value)
    else:
        values[key] = value