fix the polymorphic issue

[alexz0000]

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
• Filed the PR against the correct branch: 3.0.0 branch for changes related to OpenAPI spec 3.0. Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

Description of the PR

(details of the change, additional tests that have been done, reference to the issue for tracking, etc)

[alexz0000]

@wing328 team, could you help to review the issue and the PR? Do you think it's OK to merge the code? Thanks

[JeremyTangCD]

For the failure of the "continuous-integration/appveyor/pr" above, it has been improved in 14ffc12 at Nov. 12, 2018
This branch is just forked at Nov. 9, 2018.
So it is not caused by the committing codes, we could ignore it.

[wing328]

@AlexInGitHub Thanks for tagging me but I'm no longer involved in this project. I hope others will be able to help you out. Good luck.

[JeremyTangCD]

Hi @kenjones-cisco , could you help to review this PR? Thanks a lot.

[kenjones-cisco]

LGTM!
Thanks @AlexInGitHub

[JeremyTangCD]

@kenjones-cisco Thank you for reviewing, do you know who can help to merge this PR?

[alexz0000]

@kenjones-cisco Could you help to merge the code? since we are waiting for using the feature, thank you very much.

[kenjones-cisco]

Sorry, I'm not able to help with merge.

[alexz0000]

@kenjones-cisco Do you know who can merge the code?

[woz5999]

@webron @HugoMario Can someone please help figure out who is able to review and merge this mix?

[HugoMario]

sorry for delay guys, and thanks a lot @AlexInGitHub for PR!!!!

[motherclangercsinternal]

How is it looking on fixing the failing Petstore integration tests, please?
I have my own PR that I would like to test.

[alexz0000]

@motherclangercsinternal I remembered there should be some error messages on your PR's page