Do not see the link to an object (It is impossible to make active)

There is a button on which hang Listener

 g.gameObject.GetComponent<Button>().onClick.AddListener(() =>
 {
 _navigation.Buy(amount_on_island, item_weight, title, purchase_price);
 _navigation.open_purchase_content_and_close_trade_content();
 });

as you can see, he calls two functions, I am interested "open_purchase_content_and_close_trade_content"

its conten:

 public void open_purchase_content_and_close_trade_content()
 {
 _purchase_content.SetActive(true);
 Debug.Log(_purchase_content); // NULL
 }


 "public GameObject _purchase_content;"

Naturally it is given, that is, it appointed object. I have all navigation Built in a similar way, but in this case it is impossible to make an object active.