How can I translate an ENUM from my Avro schema for input to BigQuery?

We've got a Confluent-managed Kafka Connect installation with dozens of topics across both source and sink connectors. I've been asked to set up the BigQuery connector, and I'm having trouble with one particular field in the schema. In our schema it is an ENUM, with 2 values - both strings.

I've tried the cast, replace, drop transforms, but nothing is working - the connector has a stackoverflow exception and then a ConnectException, dying with this error:

org.apache.kafka.connect.errors.ConnectException: Schema Schema{our.namespace.doodad:STRUCT} does not correspond to a known timestamp type format

How can I translate this ENUM struct or field into something useful?

The elided element in the schema looks like this:

   {
  "default": null,
  "name": "type",
  "type": [
    "null",
    {
      "name": "EventType",
      "namespace": "our.namespace.doodad",
      "symbols": [
        "OPEN",
        "CLOSED"
      ],
      "type": "enum"
    }
  ]
},