Unity 5.6.0f2 Don't destroy on load duplicate

Hello!

I have a problem. Here is some code samples:

 public static Inventory instance { get; set; }
     private void Awake()
     {
         if (instance == null)
         {
             instance = this;
         }
         else
         {
             DestroyObject(gameObject);
         }
         DontDestroyOnLoad(this);
 }


     public static Inventory instance { get; set; }
         private void Awake()
         {
             if (instance == null)
             {
                 instance = this;
             }
             else
             {
                 Destroy(gameObject);
             }
             DontDestroyOnLoad(this);
     }

One of these codes is working, and the other is not. I do not know what the problem is and I want to know. The official guide says that you need to use the Destroy method but it does not work for me. I use the DestroyObject method instead Destroy and it's work fine. Who can explain why this happens?