[question] is.nullable SDK correlation

[eliebe-5]

We are building a tool to provision a CDS with entities based on .cdm.json files. I'm wondering what corresponds to the "is.nullable" trait in an AttributeMetadata from the SDK.

As far as I can tell is.nullable is always set when

                                    "traitReference": "is.requiredAtLevel",
                                        "arguments": [
                                            {
                                                "name": "level",
                                                "value": "none"
                                            }
                                        ]

exists, and value is set to none.

Is this always the case? Is there any documentation about these correlations that I have simply overlooked?

Thank you for any help!