object/nightwatch/44 matches the site

public static HumanMadeObject NightWatch_Brief_Text_Statement()
{
    var nightwatch = new HumanMadeObject()
        .WithContext()
        .WithId("https://linked.art/example/object/nightwatch/44")
        .WithLabel("Night Watch by Rembrandt");

    nightwatch.ReferredToBy = [
        new LinguisticObject()
            .WithClassifiedAs(Aat.MaterialsStatement, Aat.Statement)
            .WithContent("Oil on Canvas")
    ];

    return nightwatch;
}

• Metatype classification The second argument classifies the first, not the object: WithClassifiedAs(Aat.Description, Aat.Statement) says this is a Description, and Description is a kind of Statement. The Plain C# form shows the nesting.

var humanMadeObject = new HumanMadeObject
{
    Context = ["https://linked.art/ns/v1/linked-art.json"],
    Id = "https://linked.art/example/object/nightwatch/44",
    Label = "Night Watch by Rembrandt",
    ReferredToBy =
    [
        new LinguisticObject
        {
            Content = "Oil on Canvas",
            ClassifiedAs =
            [
                new Type("http://vocab.getty.edu/aat/300435429", "Material Statement")
                {
                    ClassifiedAs = [Aat.Statement],
                },
            ],
        },
    ],
};

Generated from the object the example builds: every property that is set, as object initialisers, with the vocabulary constants where a term is in the registry. The fluent helpers are a convenience, not a requirement; this form and the one as written produce the same JSON.