org.apache.kafka.connect.errors.DataException: Invalid JSON for record default value: null - apache-kafka

Question

I have a Kafka Avro Topic generated using KafkaAvroSerializer.
My standalone properties are as below.
I am using Confluent 4.0.0 to run Kafka connect.
key.converter=io.confluent.connect.avro.AvroConverter
value.converter=io.confluent.connect.avro.AvroConverter
key.converter.schema.registry.url=<schema_registry_hostname>:8081
value.converter.schema.registry.url=<schema_registry_hostname>:8081
key.converter.schemas.enable=true
value.converter.schemas.enable=true
internal.key.converter=org.apache.kafka.connect.json.JsonConverter
internal.value.converter=org.apache.kafka.connect.json.JsonConverter
internal.key.converter.schemas.enable=false
internal.value.converter.schemas.enable=false
When I run Kafka connectors for hdfs sink in standalone mode, I get this error message:
[2018-06-27 17:47:41,746] ERROR WorkerSinkTask{id=camus-email-service-0} Task threw an uncaught and unrecoverable exception (org.apache.kafka.connect.runtime.WorkerTask)
org.apache.kafka.connect.errors.DataException: Invalid JSON for record default value: null
at io.confluent.connect.avro.AvroData.defaultValueFromAvro(AvroData.java:1640)
at io.confluent.connect.avro.AvroData.toConnectSchema(AvroData.java:1527)
at io.confluent.connect.avro.AvroData.toConnectSchema(AvroData.java:1410)
at io.confluent.connect.avro.AvroData.toConnectSchema(AvroData.java:1290)
at io.confluent.connect.avro.AvroData.toConnectData(AvroData.java:1014)
at io.confluent.connect.avro.AvroConverter.toConnectData(AvroConverter.java:88)
at org.apache.kafka.connect.runtime.WorkerSinkTask.convertMessages(WorkerSinkTask.java:454)
at org.apache.kafka.connect.runtime.WorkerSinkTask.poll(WorkerSinkTask.java:287)
at org.apache.kafka.connect.runtime.WorkerSinkTask.iteration(WorkerSinkTask.java:198)
at org.apache.kafka.connect.runtime.WorkerSinkTask.execute(WorkerSinkTask.java:166)
at org.apache.kafka.connect.runtime.WorkerTask.doRun(WorkerTask.java:170)
at org.apache.kafka.connect.runtime.WorkerTask.run(WorkerTask.java:214)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
[2018-06-27 17:47:41,748] ERROR WorkerSinkTask{id=camus-email-service-0} Task is being killed and will not recover until manually restarted ( org.apache.kafka.connect.runtime.WorkerTask)
[2018-06-27 17:52:19,554] INFO Kafka Connect stopping (org.apache.kafka.connect.runtime.Connect).
When I use kafka-avro-console-consumer passing the schema registry, I get the Kafka messages deserialized.
i.e.:
/usr/bin/kafka-avro-console-consumer --bootstrap-server <kafka-host>:9092 --topic <KafkaTopicName> --property schema.registry.url=<schema_registry_hostname>:8081

Answer 1

Changing the "subscription" column's datatype to Union datatype fixed the issue. Avroconverters were able to deserialize the messages.

Answer 2

I think your Kafka key is null, which is not Avro.
Or it is some other type but malformed, and not converted to a RECORD datatype. See AvroData source code
case RECORD: {
if (!jsonValue.isObject()) {
throw new DataException("Invalid JSON for record default value: " + jsonValue.toString());
}
UPDATE According to your comment, then you can see this is true
$ curl -X GET localhost:8081/subjects/<kafka-topic>-key/versions/latest
{"subject":"<kafka-topic>-key","version":2,"id":625,"schema":"\"bytes\""}
In any case, HDFS Connect does not natively store the key, so try not deserializing the key at all rather than using Avro.
key.converter=org.apache.kafka.connect.converters.ByteArrayConverter
Also, your console consumer is not printing the key, so your test isn't adequate. You need to add --property print.key=true