条件绑定的初始值设定项必须具有可选类型,而不是“string”?

无法读取FCM通知用户数据,我正在尝试此操作-

    let userInfo = response.notification.request.content.userInfo

             if let jsonResult = userInfo as? Dictionary<String, AnyObject> //**Getting error on this line**
{

             if let notifyType = 
              jsonResult["gcm.notification.notification_type"] as? String ?? "" 
              {

                print(notifyType)           

              }
            }