fix: fix field is nullable but pydantic model created is required

[hubertshelley]

Description

fix field is nullable but pydantic field of model created is required

Motivation and Context

How Has This Been Tested?

Checklist:

• [x] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [x] I have added the changelog accordingly.
• [x] I have read the CONTRIBUTING document.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[long2ice]

Thanks! Please update changelog.md

[abondar]

Hi!

Sorry that PR got stale Could you please rebase it to actual develop?