Map with another map inside (unpredictable naming)

[Dag Stockstad]

Hi Avro aficionados,

I'm having trouble serializing a record with a nested map structure i.e. a
map within a map. The record I'm trying to send has the following structure:
{
    "event_type": "some_type",
    "data": {
        "id": "2f720f90-ea06-4248-a72e-01eea44981ed",
        "metadata": {
            "some_attr": "some_value",
            "some_map_with_unpredictable_name": {
                "some_attr": "some_value"
            }
        }
    }
}

And the schema is this:
{
    "namespace": "org.example.event.avro",
    "type": "record",
    "name": "EventNotification",
    "fields": [{
        "name": "event_type",
        "type": "string"
    }, {
        "name": "data",
        "type": {
            "type": "record",
            "name": "EventData",
            "fields": [{
                "name": "id",
                "type": "string"
            }, {
                "name": "metadata",
                "type": {
                    "type": "map",
                    "values": [
                        "int",
                        "float",
                        "string",
                        "boolean",
                        "long",
                        "null"
                    ]
                }
            }]
        }
    }]
}

The nested map (some_map_with_unpredictable_name) is causing problems
(serialization error). Is there any way I can have another map as a value
in the metadata map?

Due to the nature of the system, I cannot 100% predict the structure of the
metadata field. Can Avro accomodate these requirements or do I have to fall
back on something such as JSON for this one?

Help very appreciated (I'm a bit stuck).

Kind regards,
Dag