Object reference not set to an instance of an object

I have this game where my character collides with a door, a text shows up. In the Unity Editor, my game works fine, without any errors. However, once the game has been built as a 'Development Build', the game sends an error as soon as the game starts.

Here is my Door.cs script, attached to my door collider:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEngine.UI;
5. using UnityEngine.SceneManagement;
6.  
7. public class Door : MonoBehaviour
8. {
9.    
10.     public int LevelToLoad;
11.  
12.     private GameMaster gm;
13.  
14.     void Start() {
15.  
16.         gm = GameObject.FindGameObjectWithTag ("GameMaster").GetComponent<GameMaster> ();
17.         gm.inputGrp.SetActive (false);
18.  
19.     }
20.  
21.     void OnTriggerEnter2D(Collider2D col) {
22.  
23.         if (col.CompareTag ("Player")) {
24.  
25.             gm.inputGrp.SetActive (true);
26.             gm.inputText.text = ("[E] to enter");
27.  
28.             if (Input.GetKeyDown ("e")) {
29.  
30.                 SceneManager.LoadScene (LevelToLoad);
31.  
32.             }
33.  
34.         }
35.  
36.     }
37.  
38.     void OnTriggerStay2D(Collider2D col) {
39.  
40.         if (col.CompareTag ("Player")) {
41.  
42.             if (Input.GetKeyDown ("e")) {
43.  
44.                 SceneManager.LoadScene (LevelToLoad);
45.  
46.             }
47.  
48.         }
49.  
50.     }
51.  
52.     void OnTriggerExit2D(Collider2D col) {
53.  
54.         if (col.CompareTag ("Player")) {
55.  
56.             gm.inputGrp.SetActive (false);
57.             gm.inputText.text = (" ");
58.  
59.         }
60.  
61.  
62.     }
63.  
64. }
65.  

the variable inputGrp inside my GameMaster isn't used, it is just referenced through the unity editor.

Is it just a bug, or should I find a different way to reference my text inputGrp? Thanks you in advance!

Cheers

 

See if you can get more information about the error. It says open.

 

Here is the file that gets opened when I pres Open Log. It doesn't give any more info the the error. I checked that I didn't forget a reference or anything, and since it works fine in the Unity Editor, I can't figure out what the problem is.

 

Also, the door is meant to load a different scene when I press E, which works fine, the problem seems to be only with the GameObject inputGrp

 

Your not finding the GameMaster object, this is probably an initialization order error.

 

so how should i reference the GameMaster to fix this error?

 

I seem to have found the source of the problem, on line 17, "gm.inputGrp.SetActive (false);", probably because it is in the Start(), with the line that references the GameMaster. Removing that line fixes the errors, but I haven't found an alternate method to do "gm.inputGrp.SetActive (false);"

 

You can reorganize the script executing order for one thing, but what i tend to do is use a singleton pattern(not the best thing ever, but it's fine for small projects and solo development), set up the references on Awake and use only them on Start.