avro

AVRO-3259: Throw exception if unknown codec (#1531)

* AVRO-3259: Throw exception if unknown codec

* AVRO-3259: If codec is absent, it is assumed to be "null"

* AVRO-3259: Sync  null and exception handling with Java code

Co-authored-by: Zoltan Csizmadia <CsizmadiaZ@valassis.com>