A notification object's `item.rel` key can contain `null`

An example notification object that I've just found for my account:

{
    "id": "--snip--",
    "created": "2023-05-17T23:46:45Z",
    "status": "unread",
    "text": "Daravae added a news post to DOOM titled Merging of Any% sub-categories.",
    "item": {
        "rel": null,
        "uri": "https://www.speedrun.com/d2016/news/4139"
    }
}

Additionally, for the sake of having it out there, I'll add that there's also the new rel "thread" that is undocumented.

speedruncomorg / api

A notification object's `item.rel` key can contain `null` #165