我从Web服务获得空响应，但我想比较该空值

Question

let send: String = String(format:"http://abc.xyz/%@",userName)
    print(send)
    let url=URL(string:send)
    do
    {
        let userData = try Data(contentsOf: url!)
        let loginResponse = try JSONSerialization.jsonObject(with: userData, options: JSONSerialization.ReadingOptions.allowFragments) as! [string:Anyobject]
        print(loginResponse)
        let arr=(loginResponse["Activities"])
        if (![loginResponse["Activities"]]=NSNull)
        {
            print(arr!)

        }

如果响应不为null，那么我需要将一些对象添加到数组