Nullable String values not correct in JSON specs?

[Humancell]

Issue Summary

When importing the JSON specs into Postman and using them, there are numerous "issue" warnings that appear on various responses. Particularly the "meta" values for "next_page_url" and "previous_page_url", these are the most noticable.

It appears they are defined as a type of "String" rather that the supported array of "null or String": https://stackoverflow.com/questions/48111459/how-to-define-a-property-that-can-be-string-or-null-in-openapi-swagger

Steps to Reproduce

1. Import a JSON spec into Postman
2. Make an API call that includes meta paging properties in the response
3. Look at the top of the Postman request tab and see the "Issues" warning(s)

Exception/Log

The response body property "meta.previous_page_url" must be string

Technical details:

• twilio-oai version: 1.38.1
• open version: 3.1

[twilio-dx]

Ahoy! Thank you for opening your first issue here! If this request is regarding troubleshooting your application, please reach out to the support team via https://support.twilio.com.

[claudiachua]

Hi @Humancell , Thanks for bringing this to our attention. This issue has been added to our internal backlog to be prioritized.