Submit errors when inputs optional

[theconorodonnell]

Describe the bug
When using the calendar form control on optional inputs in bizform configuration, an error message is received after form submit when the default values are cleared from the form input.

To Reproduce
Steps to reproduce the behavior:

1. Create a kentico bizform
2. Use the calendar picker form control on an input, ensuring the input is marked as optional (required checkbox unchecked)
3. Place the configured bizform on a page builder page using the form widget
4. Navigate to the page
5. clear the calendar input and submit the form
6. the page returns an error message "Submission has failed. Please try again later."
   • There are no validation errors before submit to suggest any issue in the submitted form data
   • There are no events logged in kentico event log to explain the submit failuer

Expected behavior
When a form input is optional, it can be submitted with an empty value

Screenshots

Library Version
The issue was found while developing on Kentico v13.0.157 using the latest version of this nuget package.

Desktop (please complete the following information):

• OS: Windows 11 Pro
• Browser: Chrome
• Version: 131.0.6778.86
• SiteImprove chrome extension: version 2.0