Sorting JSON items from a site
They're not being too nit-picky. DataTask's completion handler will return nil for data when it couldn't get the data, like when the network is offline.  Force unwrapping 'data' means you deliberately crash the application when that happens.  That would be bad.
&quot;separate the business logic from the view controller&quot;: They expect you to make a data type to parse the JSON into, perhaps like this:
struct Item: Decodable {
    let id: Int
    let listId: Int
    let name: String?
}