jsonapi webform/webform return 500 status code

What is the specific Drupal core version that introduces this bug? I can't determine that from the way this issue is worded, but the wording indicates you may have this information.

I was experimenting with Drupal/Core upgrade to determine when this happened.
When I have core upgraded to 10.2.3 to 10.2.6, 10.2.7, it was still working ok.
I havent' got the chance to go through other 10.2.x version.
I was kinda in rush to apply the security update, then I upgraded directly to 10.3.14, /jsonapi/webform/webform stopped working.
Then I created another instance just to rule out my bias, upgraded to 10.4.5, the endpoint was not working either. I didnt encounter any issues in other endpoints.
I tried to refer to previous patching:
1. https://www.drupal.org/project/webform/issues/3283914 → --it has been included in the repo already.
please let me know if any other information I can provide.
Thanks

Does the problem appear in the latest development version of 6.3.x?

I tried 6.3.0-beta2, the issue showed up, haven't tried alph3 tho. will try and update the ticket.

It is best to test with the tip of the 6.3.x branch. You can check that out from Git or download the development version.

I just tested with dev branch (dev-6.3.x e4a28a7), I was able to re-produce the issue.
errors": [
{
"title": "Internal Server Error",
"status": "500",
"detail": "Symfony\\Component\\Yaml\\Parser::parse(): Argument #1 ($value) must be of type string, null given, called in /code/web/core/lib/Drupal/Component/Serialization/Yaml.php on line 37",
"links": {
"via": {
"href": "-------/jsonapi/webform/webform"
},
"info": {
"href": "https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.5.1"
}
}
}
]

I can't reproduce this bug. I tested with Drupal 10.2.7, 10.4.0, 10.4.1, 10.4.2, 10.4.3, and 10.4.4.

We need additional steps to reproduce the bug. Are other entity endpoints working on the affected site? Can you get a stack trace?

I have done extra testing, I was able to read stack trace that the issue was generated from another plugin, I removed that and the endpoint resume working. Sorry for the false alarm and thanks very much for your help.