How to determine optional or nullable fields in Apiary Documentation?

Question

I am working with an API documented using Apiary. I noticed that the response objects don't always specify which fields can be null or are optional (i.e., fields that may not be present in the response at all). Is there a standard way in Apiary to determine which fields can be nullable or optional?

For example, consider the following API response:

{
  "id": 1,
  "name": "John Doe",
  "email": null,
  "address": {
    "street": "123 Main St",
    "city": "Springfield",
    "state": null
  }
}

Here, the email and state fields are null, but it's not clear from the documentation whether these fields are always present and nullable or if they can be omitted entirely in some cases.

Is there a specific section in Apiary documentation that usually clarifies this? Or is this generally something that needs to be clarified with the API developers directly?

I have looked through Apiary's help section and scanned the entire documentation but couldn't find information specifying which fields can be null or optional.