[JAVA] Failed inheritance when generating objects with subtypes

Description

I am attempting to generate polymorphic Java model objects using a swagger 1.2 JSON file.
I've created a simple project using Gradle and a swagger example from
https://github.com/OAI/OpenAPI-Specification/blob/master/versions/1.2.md#5272-inheritance-example

When the models are generated there is no inheritance. Is there something that I am missing?

Project example uploaded here, https://github.com/jsmithe/swagger-codgen-subtype-test

Swagger-codegen version

2.2.3

Swagger declaration file content or url

https://github.com/jsmithe/swagger-codgen-subtype-test/blob/master/src/main/resources/test.json

Command line used for generation

gradle generateApi
Using Gradle build file similar to that linked in root's readme.
https://github.com/jsmithe/swagger-codgen-subtype-test/blob/master/build.gradle

Steps to reproduce

Generate model with provided test.json

Related issues/PRs

Several old issues that indicate this should be working. Started with #116

Start with the linked test.json and build.gradle, then run gradle generateApi to reproduce the generated Java models. Compare the subtype models with the inheritance example in the Swagger 1.2 specification and determine where inheritance is lost. Done means the generated models preserve the declared parent/subtype relationships.