Getting "thing you are trying to instantiate is Null when using Class Inheritance

Unity Engine
1

I have a CO class, an equipment class, and a switchboard class which inherits from equipment,

using UnityEngine;
using System.Collections;
using System.Collections.Generic;
public class CO2 {
    public List<EQUIPMENT>  equipments;
    public List<PERSONNEL>  personnel;
    public Vector2 position;
    public string coLabel ;
   

    public CO2 (string co_label,Vector2 my_pos, List<EQUIPMENT> _equipments = null, List<PERSONNEL> _personnel = null)
    {

        coLabel=co_label;
        this.equipments = _equipments == null ? new List<EQUIPMENT>() : _equipments;
        this.personnel = _personnel == null ? new List<PERSONNEL>() : _personnel;
        position= my_pos;
    }

    public CO2 ()
    {
        equipments=null;
        personnel=null;
        position= new Vector2 (0,0);
        coLabel=null;
    }

    public void AddEquipment( EQUIPMENT newequipment )
    {
        this.equipments.Add (newequipment);

    }

    public void AddPersonnel( PERSONNEL newpersonnel )
    {
        this.personnel.Add (newpersonnel);
    }
}

using UnityEngine;
using System.Collections;

public class EQUIPMENT {
    public Transform obj;
    public Vector3 obj_pos;
    public int maintenence_cost;
    public int max_subs;

    public EQUIPMENT ()
    {
        obj = null;
        obj_pos = new Vector3(0,0,0);
        maintenence_cost = 123;
        max_subs=123;
    }
   
    public EQUIPMENT (Transform new_object, Vector3 new_object_pos, int new_cost, int new_max_subs)
    {
        obj = new_object;
        obj_pos = new_object_pos;
        maintenence_cost = new_cost;
        max_subs=new_max_subs;
        }
}

using UnityEngine;
using System.Collections;

public class SWITCHBOARD : EQUIPMENT {



   
    public SWITCHBOARD (Transform new_object, Vector3 new_object_pos)
    {

        maintenence_cost = 1160;
        max_subs=52;
        }
}

in my main script I have this

    city.centralOffice.AddEquipment (new EQUIPMENT (test_prefab, Newposition, test_maintenence_cost, 10000));
city.centralOffice.AddEquipment (new SWITCHBOARD (switchboard_prefab, Newposition));

Elsewhere in the main script I have this

        foreach (EQUIPMENT e in city.centralOffice.equipments) {
            Instantiate (e.obj, e.obj_pos, transform.rotation);

it works fine for the test_prefab but for switchboard_prefab I get error
ArgumentException: The thing you want to instantiate is null

2

on your constructor of your class SWITCHBOARD, you don’t use the transfrom and the vector3.

try this instead :

  public SWITCHBOARD (Transform new_object, Vector3 new_object_pos)
    {
        maintenence_cost = 1160;
        max_subs=52;
        base.obj = new_object;
      base.obj_pos = new_object_pos;

        }
3

you can call the base constructor too :

  public SWITCHBOARD (Transform new_object, Vector3 new_object_pos)
: base(new_object,new_object_pos,1160,123)
    {   }