NPE when a schema isn't found in a schema registry

[vordimous]

Describe the bug

zilla-demo.schema-registry [31/Jul/2024:18:02:20 +0000] CATALOG_KARAPACE_SCHEMA_REGISTRY_UNRETRIEVABLE_SCHEMA_SUBJECT_VERSION Unable to fetch schema for subject core-paymenthub-simple-pay-ipn-request-value with version latest.
org.agrona.concurrent.AgentTerminationException: java.lang.NullPointerException: Cannot invoke "io.aklivity.zilla.runtime.model.avro.internal.avro.Schema.getType()" because "schema" is null
    at io.aklivity.zilla.runtime.engine@0.9.89/io.aklivity.zilla.runtime.engine.internal.registry.EngineWorker.doWork(EngineWorker.java:841)
    at org.agrona.core/org.agrona.concurrent.AgentRunner.doWork(AgentRunner.java:304)
    at org.agrona.core/org.agrona.concurrent.AgentRunner.workLoop(AgentRunner.java:296)
    at org.agrona.core/org.agrona.concurrent.AgentRunner.run(AgentRunner.java:162)
    at java.base/java.lang.Thread.run(Thread.java:1570)
Caused by: java.lang.NullPointerException: Cannot invoke "io.aklivity.zilla.runtime.model.avro.internal.avro.Schema.getType()" because "schema" is null
    at io.aklivity.zilla.runtime.model.avro@0.9.89/io.aklivity.zilla.runtime.model.avro.internal.AvroWriteConverterHandler.serializeJsonRecord(AvroWriteConverterHandler.java:90)
    at io.aklivity.zilla.runtime.catalog.schema.registry@0.9.89/io.aklivity.zilla.runtime.catalog.schema.registry.internal.handler.SchemaRegistryCatalogHandler.encode(SchemaRegistryCatalogHandler.java:318)
    at io.aklivity.zilla.runtime.model.avro@0.9.89/io.aklivity.zilla.runtime.model.avro.internal.AvroWriteConverterHandler.convert(AvroWriteConverterHandler.java:67)
    at io.aklivity.zilla.runtime.binding.kafka@0.9.89/io.aklivity.zilla.runtime.binding.kafka.internal.cache.KafkaCachePartition.writeProduceEntryContinue(KafkaCachePartition.java:869)
    at io.aklivity.zilla.runtime.binding.kafka@0.9.89/io.aklivity.zilla.runtime.binding.kafka.internal.stream.KafkaCacheClientProduceFactory$KafkaCacheClientProduceFan.onClientInitialData(KafkaCacheClientProduceFactory.java:733)
    at io.aklivity.zilla.runtime.binding.kafka@0.9.89/io.aklivity.zilla.runtime.binding.kafka.internal.stream.KafkaCacheClientProduceFactory$KafkaCacheClientProduceStream.onClientInitialData(KafkaCacheClientProduceFactory.java:1354)
    at io.aklivity.zilla.runtime.binding.kafka@0.9.89/io.aklivity.zilla.runtime.binding.kafka.internal.stream.KafkaCacheClientProduceFactory$KafkaCacheClientProduceStream.onClientMessage(KafkaCacheClientProduceFactory.java:1276)
    at io.aklivity.zilla.runtime.engine@0.9.89/io.aklivity.zilla.runtime.engine.internal.registry.EngineWorker.handleReadInitial(EngineWorker.java:1260)
    at io.aklivity.zilla.runtime.engine@0.9.89/io.aklivity.zilla.runtime.engine.internal.registry.EngineWorker.handleRead(EngineWorker.java:1227)
    at io.aklivity.zilla.runtime.engine@0.9.89/io.aklivity.zilla.runtime.engine.internal.concurent.ManyToOneRingBuffer.read(ManyToOneRingBuffer.java:229)
    at io.aklivity.zilla.runtime.engine@0.9.89/io.aklivity.zilla.runtime.engine.internal.registry.EngineWorker.doWork(EngineWorker.java:835)
    ... 4 more
    Suppressed: java.lang.Exception: [engine/data#1]        [0x010100000000001b] streams=[consumeAt=0x00003550 (0x0000000000003550), produceAt=0x00003550 (0x0000000000003550)]
            at io.aklivity.zilla.runtime.engine@0.9.89/io.aklivity.zilla.runtime.engine.internal.registry.EngineWorker.doWork(EngineWorker.java:839)
            ... 4 more
org.agrona.concurrent.AgentTerminationException: java.lang.NullPointerException: Cannot invoke "io.aklivity.zilla.runtime.engine.binding.function.MessageConsumer.accept(int, org.agrona.DirectBuffer, int, int)" because "receiver" is null
    at io.aklivity.zilla.runtime.engine@0.9.89/io.aklivity.zilla.runtime.engine.internal.registry.EngineWorker.doWork(EngineWorker.java:841)
    at org.agrona.core/org.agrona.concurrent.AgentRunner.doWork(AgentRunner.java:304)
    at org.agrona.core/org.agrona.concurrent.AgentRunner.workLoop(AgentRunner.java:296)
    at org.agrona.core/org.agrona.concurrent.AgentRunner.run(AgentRunner.java:162)
    at java.base/java.lang.Thread.run(Thread.java:1570)
Caused by: java.lang.NullPointerException: Cannot invoke "io.aklivity.zilla.runtime.engine.binding.function.MessageConsumer.accept(int, org.agrona.DirectBuffer, int, int)" because "receiver" is null
    at io.aklivity.zilla.runtime.binding.kafka@0.9.89/io.aklivity.zilla.runtime.binding.kafka.internal.stream.KafkaCacheBootstrapFactory.doEnd(KafkaCacheBootstrapFactory.java:273)
    at io.aklivity.zilla.runtime.binding.kafka@0.9.89/io.aklivity.zilla.runtime.binding.kafka.internal.stream.KafkaCacheBootstrapFactory$KafkaBootstrapMetaStream.doMetaInitialEnd(KafkaCacheBootstrapFactory.java:1176)
    at io.aklivity.zilla.runtime.binding.kafka@0.9.89/io.aklivity.zilla.runtime.binding.kafka.internal.stream.KafkaCacheBootstrapFactory$KafkaBootstrapMetaStream.doMetaInitialEndIfNecessary(KafkaCacheBootstrapFactory.java:1167)
    at io.aklivity.zilla.runtime.binding.kafka@0.9.89/io.aklivity.zilla.runtime.binding.kafka.internal.stream.KafkaCacheBootstrapFactory$KafkaBootstrapStream.onBootstrapInitialEnd(KafkaCacheBootstrapFactory.java:495)
    at io.aklivity.zilla.runtime.binding.kafka@0.9.89/io.aklivity.zilla.runtime.binding.kafka.internal.stream.KafkaCacheBootstrapFactory$KafkaBootstrapStream.onBootstrapInitial(KafkaCacheBootstrapFactory.java:439)
    at io.aklivity.zilla.runtime.engine@0.9.89/io.aklivity.zilla.runtime.engine.binding.function.MessageConsumer.lambda$andThen$0(MessageConsumer.java:82)
    at io.aklivity.zilla.runtime.engine@0.9.89/io.aklivity.zilla.runtime.engine.internal.registry.EngineWorker.handleReadInitial(EngineWorker.java:1263)
    at io.aklivity.zilla.runtime.engine@0.9.89/io.aklivity.zilla.runtime.engine.internal.registry.EngineWorker.handleRead(EngineWorker.java:1227)
    at io.aklivity.zilla.runtime.engine@0.9.89/io.aklivity.zilla.runtime.engine.internal.concurent.ManyToOneRingBuffer.read(ManyToOneRingBuffer.java:229)
    at io.aklivity.zilla.runtime.engine@0.9.89/io.aklivity.zilla.runtime.engine.internal.registry.EngineWorker.doWork(EngineWorker.java:835)
    ... 4 more
    Suppressed: java.lang.Exception: [engine/data#2]        [0x0102000000000003] streams=[consumeAt=0x0001d078 (0x000000000001d078), produceAt=0x0001d4d8 (0x000000000001d4d8)]
            at io.aklivity.zilla.runtime.engine@0.9.89/io.aklivity.zilla.runtime.engine.internal.registry.EngineWorker.doWork(EngineWorker.java:839)
            ... 4 more

To Reproduce
Steps to reproduce the behavior:

1. Run the http.kafka.karapace
2. POST an object without registering a schema
3. Zilla crashes with NPE