From what can be an error in the selective menu?

Question

Unity

In general, in my code there is a selective menu for choosing languages, after choosing a language in (On Value Changet (Int32)) I use the following method

public  int Language = 0;
public GameObject DropdownLanguage;
public void SetLanguage(){
        Language = DropdownLanguage.GetComponent<Dropdown>().value;
        PlayerPrefs.SetInt("Language", Language);
        PlayerPrefs.Save();
        }

It worked properly without any bugs, and then during the next test I got this error 3 times

spoiler

NullReferenceException: Object reference not set to an instance of an object
UnityEngine.UI.Dropdown.AlphaFadeList
(System.Single duration, System.Single start, System.Single end)
(at C:/Program Files/Unity/Hub/Editor/2020.2.1f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/UI/Core/Dropdown.cs:1049)
UnityEngine.UI.Dropdown.Show ()
(at C:/Program Files/Unity/Hub/Editor/2020.2.1f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/UI/Core/Dropdown.cs:866)
UnityEngine.UI.Dropdown.OnPointerClick (UnityEngine.EventSystems.PointerEventData eventData)
(at C:/Program Files/Unity/Hub/Editor/2020.2.1f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/UI/Core/Dropdown.cs:685)
UnityEngine.EventSystems.ExecuteEvents.Execute (UnityEngine.EventSystems.IPointerClickHandler handler, UnityEngine.EventSystems.BaseEventData eventData)
(at C:/Program Files/Unity/Hub/Editor/2020.2.1f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/EventSystem/ExecuteEvents.cs:50)
UnityEngine.EventSystems.ExecuteEvents.Execute[T]
(UnityEngine.GameObject target, UnityEngine.EventSystems.BaseEventData eventData, UnityEngine.EventSystems.ExecuteEvents+EventFunction`1[T1] functor)
(at C:/Program Files/Unity/Hub/Editor/2020.2.1f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/EventSystem/ExecuteEvents.cs:262)
UnityEngine.EventSystems.EventSystem:Update() (at C:/Program Files/Unity/Hub/Editor/2020.2.1f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/EventSystem/EventSystem.cs:385)

while the selective menu itself hung and did not disappear.
I stopped the test and started it again, I didn’t even change anything, no more errors popped up, and now I’ve been checking without changes and no errors yet ...

So I didn’t understand why this error got out, whether it will come out again when any ...
What tell me in this case?

Answer 1

Something didn't initialize somewhere.
If the tests are automatic - it is quite possible that you need to insert an expectation of SOMETHING (but not in time!) - such as the same Start or Awake
In general, you need to look at the logic and look at the crash site