Deleting assignments using REST API

Followed https://docs.microsoft.com/en-us/rest/api/blueprints/assignments/delete to find a way to delete assignments using REST APIs. The issue is that, when I use the API to delete the non-existent assignments without using the deleteBehavior param, it throws 204 - No Content error, which is right. But the same API when used with deleteBehavior param for deleting a non-existent assignment, it returns 202 status code.

[alex-frankel]

This does look like it could be a bug, but we are not likely to get this resolved unless it is causing a severe blocking issues. The Blueprints service is going to be taking a dependency on Template Specs and Deployment stacks to replace the blueprint definition and assignment respectively. Have you heard about either of those?

Out of curiosity, are you using the blueprint locks capability?

Could you please tell if there is any documentation that I can go through to understand how to create blueprint service using Template Specs and Deployment Stacks?
I'm not using the blueprint locks capability.