using System;

using System.Linq;

using System.Collections.Generic;

using System.Diagnostics;

​

public class Program

{

    public class GameObject{

        public string name;

    }

   public class SetupWeapon {

​

        public int poolSize;

        public GameObject prefab;

​

        public SetupWeapon(int size, GameObject goPrefab) {

            this.poolSize = size;

            this.prefab = goPrefab;

        }

    }

        public int[] AttackIDs {

        get {

            var toArray = _weaponData.Select(a => a.Key).ToArray();

            return toArray;

        }

    }

    private int[] PoolSize {

        get {

            var toArray = _weaponData.Select(a => a.Value.poolSize).ToArray();

            return toArray;

        }

    }

    private GameObject[] Prefab {

        get {

            var toArray = _weaponData.Select(a => a.Value.prefab).ToArray();

            return toArray;

        }

    }

    public Dictionary<int, SetupWeapon> _weaponData = new Dictionary<int, SetupWeapon>();

    public void Start () {

​

        for (int i = 0; i < AttackIDs.Length; i++){

            Console.WriteLine(AttackIDs[i]); // works just fine

            Console.WriteLine(_weaponData[0].poolSize); // works just fine

            Console.WriteLine(_weaponData[0].prefab.name); // works just fine

            Console.WriteLine(PoolSize[0]); // NullReferenceException

            Console.WriteLine(Prefab[0].name); // NullReferenceException

        }

    }

    public static void Main()

    {

        var p = new Program();

        p._weaponData.Add(0, new SetupWeapon(0, new GameObject(){ name = "0"}));

        p._weaponData.Add(1, null);  // this will cause null exception

        p._weaponData.Add(2, new SetupWeapon(2, null)); // this will not

​

        p.Start();

    }

}