Why isn't the variable being assigned?

I'm using the unity debugger to find out why a variable isn't being changed. What I found was very strange.

The yellow mark is where the code execution currently is. So the variable hold should be assigned. The position 8,2,2 in map indeed holds a character object according to the debugger. However, hold which is assigned to map[8,2,2] does not have a reference to a character object, instead it has one to a null obj.

So my question is, why isn't the variable being assigned properly?

Edit:

You can see that there is an object at map[8,2,2] already. The problem is that hold isn't being assigned to the value at 8,2,2. Instead it is being assigned to a different Entity, which holds a reference to a null object.

Edit #2 (added code for Entity class)

 using UnityEngine;
 using System.Collections;
 using Newtonsoft.Json;
 
 [JsonObject(MemberSerialization.OptIn)]
 public class Entity : System.IEquatable<Entity>
 {
     [JsonProperty]
     public int x;
     [JsonProperty]
     public int y;
     [JsonProperty]
     public int z;
     [JsonProperty]
     public states type;
     
     public GameObject obj;
     
     public Entity()
     {
         obj = null;
         this.type=states.empty;
     }
     
     public Entity(GameObject reference, states type)
     {
         obj = reference;
         x = (int) obj.transform.position.x;
         y = (int) obj.transform.position.y;
         z = (int) obj.transform.position.z;
         this.type = type;
     }
     
     public bool Equals(Entity other)
     {
         return this.x==other.x&&this.y==other.y
             &&this.z==other.z&&this.type==other.type;
     }
             
     public string getCoordinatesasString()
     {
         return x.ToString()+','+y.ToString()+','+z.ToString()+','+type.ToString();
     }    
         
     public Vector3 getCoordinates()
     {
         return new Vector3(x,y,z);
     }
     
     public void setData(int x, int y, int z, states type)
     {
         this.x=x;
         this.y=y;
         this.z=z;
         this.type=type;
     }
     
 }