On build() method of AvroSchemaBuilder class, the ARRAY case assumes that elementSchema field is instance of AvroSchema class, as it is declared as Schema, and method "withElementSchema" set directly with a schema.

To fix it, schema should be declared as AvroSchema and withElementSchema method should convert schema to AvroSchema if instance is not yet of this type.
(same with Schema.Entry.getElementSchema() on "withEntry" method)
Easy to show with unit test; not easy to fix.