Fixes a regression in kafka serialization that causes run-time panics. The deserializer can only deserialize value schemas (as it has logic to project out the non-timestamp columns). In the Kafka producer, we had logic to also serialize the keys if they were present. That was previously ignored, because there never ends up being a key in the graph produced by SQL. However, when we changed the key representation to be an Option<Vec<usize>>, that is now Some but with an empty schema, causing the key serialization code to run but panic due to not having any columns.
Fixes a regression in kafka serialization that causes run-time panics. The deserializer can only deserialize value schemas (as it has logic to project out the non-timestamp columns). In the Kafka producer, we had logic to also serialize the keys if they were present. That was previously ignored, because there never ends up being a key in the graph produced by SQL. However, when we changed the key representation to be an
Option<Vec<usize>>, that is now Some but with an empty schema, causing the key serialization code to run but panic due to not having any columns.