Swift MutableDocument's collection is not set when a new document is saved

    func testGetCollectionAfterDocIsSaved() throws {

        let col1 = try db.createCollection(name: "collection1")

        var doc = MutableDocument(id: "doc1")

        doc.setString("hello", forKey: "greeting")

        try col1.save(document: doc)

        XCTAssert(doc.collection == col1)

    }