Avro Record Constructor

AvroRecord constructor build delegate with inner delegate schema.

delegate = new GenericData.Record(this.schema.getDelegate());

This delegate can be an union type between null & record (in case of a nullable entry), and lead to avro exception.
code should use actualDelegate instead (which unwrap union type in case of nullable entry)

delegate = new GenericData.Record(this.schema.getActualDelegate());