For nullable aware programming languages like Kotlin it's nice if the OpenAPI spec is explicit about properties that are never null so null safe code can be generated. It looks like required is already being documented for request parameters and bodies, but not for response bodies.

An example is https://docs.camunda.org/manual/latest/reference/rest/process-definition/post-start-process-instance. I don't think "id" in the response is ever supposed to be missing. If so, it would be nice if ProcessInstanceWithVariablesDto has "id" in the required list.