My game objects seems to be not initialized, how can I initialize objects in Unity

Question

I am trying to set different values variable for each object that I touch, and for some reason, I get that object is null - like not initialized!

The following is the code:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;


public class DragBall : MonoBehaviour {

    public GameObject gameObjectToDrag;

    public Text txt;

    public Vector3 GOcenter;
    public Vector3 touchPosition;
    public Vector3 offset;
    public Vector3 newGOcenter;

    RaycastHit hit;

    public int value;

    public bool draggingMode = false;

    // Use this for initialization
    void Start () {
        if (this.gameObjectToDrag != null)
        {
            if (this.gameObjectToDrag.name == "Ball1")
            {
                this.value = 1;
            }
            else if (this.gameObjectToDrag.name == "Ball2")
            {
                this.value = 2;
            }
            else if (this.gameObjectToDrag.name == "Ball3")
            {
                this.value = 3;
            }
        }
        else {
            this.txt.text = "object is null";
        }
    }

    // Update is called once per frame
    void Update () {

        if (Input.GetMouseButtonDown(0)) {
            Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
            if (Physics.Raycast(ray, out hit))
            {
                this.gameObjectToDrag = hit.collider.gameObject;
                GOcenter = this.gameObjectToDrag.transform.position;
                touchPosition = Camera.main.ScreenToWorldPoint(Input.mousePosition);
                offset = touchPosition - GOcenter;
                draggingMode = true;
            }
        }

        if (Input.GetMouseButton(0)) {
            if (draggingMode) {
                touchPosition = Camera.main.ScreenToWorldPoint(Input.mousePosition);
                newGOcenter = touchPosition - offset;

                if (this.gameObjectToDrag.name == "Ball1") {
                    this.gameObjectToDrag.transform.position = new Vector3(newGOcenter.x, 1, newGOcenter.z); // 0 means Y axis , so let the ball go horizontally only
                }
                else if (this.gameObjectToDrag.name == "Ball2")
                {
                    this.gameObjectToDrag.transform.position = new Vector3(newGOcenter.x, 2, newGOcenter.z); // 0 means Y axis , so let the ball go horizontally only
                }
                else if (this.gameObjectToDrag.name == "Ball3")
                {
                    this.gameObjectToDrag.transform.position = new Vector3(newGOcenter.x, 3, newGOcenter.z); // 0 means Y axis , so let the ball go horizontally only
                }

            }
            this.txt.text = this.value + "";
        }

        if (Input.GetMouseButtonUp(0)) {
            draggingMode = false;
        }
    }
}

How do I make sure that the object is initialized and that I can set different values for each object for the public int value property?

Edit Code:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;


public class DragBall : MonoBehaviour {

    public GameObject gameObjectToDrag;

    public Text txt;

    private int value;

    public Vector3 GOcenter;
    public Vector3 touchPosition;
    public Vector3 offset;
    public Vector3 newGOcenter;

    RaycastHit hit;

    public bool draggingMode = false;

    // Use this for initialization
    void Start () {
        if (this.gameObject.name == "Ball1")
        {
            this.value = 1;
            Debug.Log("BALL 1 VALUE SET TO " + value);
        }
        else if (this.gameObject.name == "Ball2")
        {
            this.value = 2;
            Debug.Log("BALL 2 VALUE SET TO " + value);
        }
        else if (this.gameObject.name == "Ball3")
        {
            this.value = 3;
            Debug.Log("BALL 3 VALUE SET TO " + value);
        }
    }

    // Update is called once per frame
    void Update () {

        if (Input.GetMouseButtonDown(0))
        {
            Debug.Log("Mouse is pressed down");
            Camera cam = Camera.main;

            //Raycast depends on camera projection mode
            Vector2 origin = Vector2.zero;
            Vector2 dir = Vector2.zero;

            if (cam.orthographic)
            {
                origin = Camera.main.ScreenToWorldPoint(Input.mousePosition);
            }
            else
            {
                Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
                origin = ray.origin;
                dir = ray.direction;
            }

            RaycastHit2D hit = Physics2D.Raycast(origin, dir);

            //Check if we hit anything
            if (hit)
            {
                Debug.Log("We hit " + hit.collider.name);

                this.gameObjectToDrag = hit.collider.gameObject;
                GOcenter = this.gameObjectToDrag.transform.position;
                touchPosition = Camera.main.ScreenToWorldPoint(Input.mousePosition);
                offset = touchPosition - GOcenter;
                draggingMode = true;
            }
        }

        if (Input.GetMouseButton(0))
        {
            if (draggingMode)
            {
                touchPosition = Camera.main.ScreenToWorldPoint(Input.mousePosition);
                newGOcenter = touchPosition - offset;

                if (this.gameObjectToDrag.name == "Ball1")
                {
                    this.gameObjectToDrag.transform.position = new Vector3(newGOcenter.x, 1, newGOcenter.z); // 0 means Y axis , so let the ball go horizontally only
                }
                else if (this.gameObjectToDrag.name == "Ball2")
                {
                    this.gameObjectToDrag.transform.position = new Vector3(newGOcenter.x, 2, newGOcenter.z); // 0 means Y axis , so let the ball go horizontally only
                }
                else if (this.gameObjectToDrag.name == "Ball3")
                {
                    this.gameObjectToDrag.transform.position = new Vector3(newGOcenter.x, 3, newGOcenter.z); // 0 means Y axis , so let the ball go horizontally only
                }

            }
        }

        if (Input.GetMouseButtonUp(0))
        {
            draggingMode = false;
        }

    }
}