ClassCastException with Spring Cloud Stream Kafka Streams

Question

I'm running into a problem that's almost identical to another StackOverflow question, but the solution provided doesn't work for me.

The error I'm getting (at runtime):

2022-09-14 11:53:49,301 [ERROR] [scheduling-1] BindingService - Failed to create producer binding; retrying in 30 seconds {}
java.lang.ClassCastException: class com.sun.proxy.$Proxy152 cannot be cast to class org.springframework.messaging.MessageChannel (com.sun.proxy.$Proxy152 and org.springframework.messaging.MessageChannel are in unnamed module of loader 'app')
        at org.springframework.cloud.stream.binder.AbstractMessageChannelBinder.doBindProducer(AbstractMessageChannelBinder.java:92) ~[spring-cloud-stream-3.2.4.jar:3.2.4]
        at org.springframework.cloud.stream.binder.AbstractBinder.bindProducer(AbstractBinder.java:152) ~[spring-cloud-stream-3.2.4.jar:3.2.4]
        at org.springframework.cloud.stream.binding.BindingService.lambda$rescheduleProducerBinding$4(BindingService.java:351) ~[spring-cloud-stream-3.2.4.jar:3.2.4]
        at org.springframework.scheduling.support.DelegatingErrorHandlingRunnable.run(DelegatingErrorHandlingRunnable.java:54) [spring-context-5.3.22.jar:5.3.22]
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515) [?:?]
        at java.util.concurrent.FutureTask.run(FutureTask.java:264) [?:?]
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304) [?:?]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) [?:?]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) [?:?]
        at java.lang.Thread.run(Thread.java:829) [?:?]

But my build.gradle.kts has:

    implementation("org.apache.avro:avro:1.11.0")
    implementation("io.confluent:kafka-avro-serializer:7.2.1")
    implementation("io.confluent:kafka-streams-avro-serde:7.2.1")
    implementation("org.springframework.cloud:spring-cloud-starter-stream-kafka:3.2.5")
    implementation ("org.springframework.cloud:spring-cloud-stream-binder-kafka-streams:3.2.5")

I've tried altering my function around to be a consumer, producer, or function, and the only thing that changes is if it's a "producer binding" or a "consumer binding" that throws the exception on the BindingService.

   @Bean
    public Function<KStream<String, InboundObject>, KStream<String, OutboundObject>> streamFunction() {
        return input -> {
            return input.map((k, v) -> new KeyValue<>(null, null));
        };
    }

For Serde, I'm using Avro:

default.value.serde: io.confluent.kafka.streams.serdes.avro.GenericAvroSerde

        binder:
          producer-properties:
            key.serializer: org.apache.kafka.common.serialization.StringSerializer
            value.serializer: io.confluent.kafka.serializers.KafkaAvroSerializer
            schema.registry.url: http://localhost:9091
          consumer-properties:
            key.deserializer: org.apache.kafka.common.serialization.StringDeserializer
            value.deserializer: io.confluent.kafka.serializers.KafkaAvroDeserializer
            schema.registry.url: http://localhost:9091
            specific.avro.reader: true

ClassCastException with Spring Cloud Stream Kafka Streams

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