Avro Record : array containing Null.

Issues like TDI-47550 are about Record with array field that contains null elements.
As it work well with RecordImpl, it does not with AvroRecord.
(elementSchema doesn't allow null)

The trap here is that element schema is define in schema class; when schema.type is an Array (for root object as example) and in Entry, when the field type is an Array.

This should be fix in

• AvroSchemaBuilder.withElementSchema method (convert X -> Union(X, NULL) if X is not union). Then be careful to affect good schema to new Record that come into array (Type NULL or Type X).

• Create a new class to extends EntryImpl.BuilderImpl to review withElementSchema method