test/org/apache/pig/builtin/avro/schema/nullableRecordInMap.avsc

{
    "name" : "nullableRecordInMap",
    "namespace" : "org.apache.pig.test.builtin",
    "type" : "record",
    "fields" : [
        {"name" : "key", "type" : "string"},
        {"name" : "value", "type" : "int"},
        {
            "name" : "parameters",
            "type": [
                "null",
                {
                    "type": "map",
                    "values": [
                        "null",
                        {
                            "type": "record",
                            "name": "nullable_record",
                            "fields": [
                                {
                                    "name": "id",
                                    "type": [
                                        "null",
                                        "string"
                                    ]
                                }
                            ]
                        }
                    ]
                }
            ]
        }
    ]
}