[Java] Inherited properties are evicted when using oneOf.

Description

IF Pet object defines a petType property
AND Cat and Dog include Pet through the allOf
AND APet object includes both Cat and Dog through the oneOf
THEN property petType is missing from the object APet

Swagger-codegen version

Online version AND swagger-codegen-cli-3.0.0-20180717.153005-90.jar

Swagger declaration

openapi: 3.0.0
info:
  version: 0.0.0
  title: Example
paths:
  /randomPet:
    get:
      responses:
        '200':
          description: Random pet
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/APet'
components:
  schemas:
    APet:
      oneOf:
        - $ref: '#/components/schemas/Cat'
        - $ref: '#/components/schemas/Dog'
      discriminator:
        propertyName: petType
    Pet:
      type: object
      required:
        - petType
      properties:
        petType: { type: string }
    Dog:
      allOf:
        - $ref: '#/components/schemas/Pet'
        - type: object
          properties:
            bark: { type: boolean }
    Cat:
      allOf:
        - $ref: '#/components/schemas/Pet'
        - type: object
          properties:
            age: { type: number }

Resulting Java Bean

(with everything else stripped)

public class APet {
  private BigDecimal age = null;
  private Boolean bark = null;
}

Expected Java Bean

This part is tricky. In principle, I'd rather have just a Pet object that could be further casted into a Cat or a Dog. In this case the object APet should not even exist. But at the very minimum, the property must not be lost:

public class APet {
  private BigDecimal age = null;
  private Boolean bark = null;
  private String petType = null;
}

or

public class APet extends Pet {
  private BigDecimal age = null;
  private Boolean bark = null;
}

Command line used for generation

java -jar swagger-codegen-cli-3.0.0-20180717.153005-90.jar generate -DhideGenerationTimestamp=true -l java -i openapi.yaml

Related issue:

https://github.com/swagger-api/swagger-codegen/issues/8441