Question Object reference not set to an instance of an object

Hello Guys,
I am trying to access variable : missionName from my AKMissionData script to AKMissionSystem script.
But getting error : Object reference not set to an instance of an object.
Please Help!!!

Code (CSharp):

1. public class AKMissionData : MonoBehaviour
2. {
3.     //Mission Info
4.     public int missionOrder;
5.     public string missionName;
6.     public string missionDescription;
7.  
8.     public GameObject missionGiver;
9.  
10.     public int missionTimer;
11.     public int missionReward;
12.  
13.     public enum types { Reach, Kill, Gather, Save, Defend }
14.  
15.     public types missionType;
16.     public GameObject missiontarget;
17.     public int  missionTargetAmount;
18.     public bool missionStartWithGame;
19.     // Start is called before the first frame update
20.     void Start()
21.     {
22.         missionName = "mission Name Here";
23.     }
24.  
25.     // Update is called once per frame
26.     void Update()
27.     {
28.      
29.     }
30. }
31.  

Trying to get variable from above script to below script :

Code (CSharp):

1. public class AKMissionSystem : MonoBehaviour
2. {
3.     [Header("Mission UI")]
4.     public Text missionInfoTxt;
5.     private string missionName;
6.  
7.  
8.  
9.     void Start()
10.     {
11.         GameObject go = GameObject.FindGameObjectWithTag("MissionData");
12.         missionName = go.GetComponent<AKMissionData>().missionName;
13.      
14.         Debug.Log(missionName);
15.         missionInfoTxt.text = missionName;
16.  
17.     }
18.  
19.  
20.  
21. }

Error :
NullReferenceException: Object reference not set to an instance of an object
AKMissionSystem.Start () (at Assets/AKMissionSystem.cs:17)

 

How to fix a NullReferenceException in Unity3D:

http://plbm.com/?p=221