def METHOD_NAME(self, validated_data):
    if "filter_string" in validated_data.keys():
        filter_string_dict = json.loads(validated_data.pop("filter_string"))
        if "filter" not in validated_data.keys():
            validated_data["filter"] = filter_string_dict
        else:
            filter_dict = validated_data["filter"]
            source_system_ids = filter_string_dict["sourceSystemIds"]
            if source_system_ids and ("sourceSystemIds" not in filter_dict.keys()):
                validated_data["filter"]["sourceSystemIds"] = source_system_ids
            tags = filter_string_dict["tags"]
            if tags and "tags" not in filter_dict.keys():
                validated_data["filter"]["tags"] = tags
    return validated_data