private String fieldTypeToSchemaType(FieldSpec field,
                                         short version,
                                         Versions fieldFlexibleVersions) {
        return fieldTypeToSchemaType(field.type(),
            field.nullableVersions().contains(version),
            version,
            fieldFlexibleVersions,
            field.zeroCopy());
    }
The versions that implement a KIP-482 flexible schema.
generator/src/main/java/org/apache/kafka/message/SchemaGenerator.java