Probably Kafka DA produces '\0' in the end of TEXT or VARCHAR with width > 7

The customer has several columnstore tables, with the default charset set to utf8mb4. The tables are populated via kafka & the kafka-avro-adapter.
All strings in the table get a \0 at the end, when populated this way, here is an example:

1043682 node\0 job_per_template\0 node/1043682\0 Default\0 0 2019-02-25 08:33:57 1 \0 \0 \0 \0 \0 Mozilla/5.0 (Linux; Android 6.0.1; Nexus 5X Build/MMB29P) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2272.96 Mobile Safari/537.36 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)\0

The entries look ok when viewed with the kafka-avro-console-consumer, so I guess there must be a problem in the kafka-avro-adapter.
Is there any config I have to set, or anyone has a good idea how to debug the issue in the adapter?

Here is the actual Google Groups topic describing the problem.

1. https://groups.google.com/forum/#!topic/mariadb-columnstore/CCNy365GSUw