TableTopic’s Avro-to-Iceberg RecordBinder instantiates binders only for top-level STRUCT columns; LIST or MAP elements that are STRUCT fall back to convert() without a nested binder and blow up with java.io.IOException: java.lang.ClassCastException: class org.apache.avro.generic.GenericData$Record cannot be cast to class org.apache.iceberg.data.Record.

In protobuf mode every map<K,V> is normalized into list<struct<key:K,value:V>>, so even map<string,string> becomes a LIST whose element type is STRUCT and hits the same crash.

Any ingestion job that produces LIST<STRUCT<…>> or MAP<*, STRUCT<…>> data therefore fails on 1.6.0 before records reach Iceberg.