Unity NullReferenceException is the object of class Die Im creating actually Null and how do I fix this issue?

Question

I'm new to unity and have a question regarding a segment of code I'm having trouble with. When I declare the object in the main script it properly renders the Blank sprite but when I try calling the PlaceMultiplier function it throws the NullReferenceException. Im hoping to get the fix and also learn from the explanation, thanks!

using UnityEngine; using System.Collections;

public class Die : MonoBehaviour {

public Sprite Dice1;
public Sprite Blank;
public Sprite Multiplier1;
public Sprite Multiplier2;
public Sprite Multiplier3;
public Sprite Multiplier4;
public Sprite Multiplier5;
public Sprite Multiplier6;
public Sprite Multiplier7;
public Sprite Multiplier8;


// Use this for initialization
void Start () {

    if ((this != null)) {
        this.gameObject.GetComponent<SpriteRenderer> ().sprite = Blank;
    }

}

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

}

public void PlaceMultiplier(int multiple){


    if (multiple == 2) {
        this.gameObject.GetComponent<SpriteRenderer> ().sprite = Multiplier1;
    }

    if (multiple == 3) {
        this.gameObject.GetComponent<SpriteRenderer> ().sprite = Multiplier2;
    }

    if (multiple == 7) {
        this.gameObject.GetComponent<SpriteRenderer> ().sprite = Multiplier3;
    }

    if (multiple == 8) {
        this.gameObject.GetComponent<SpriteRenderer> ().sprite = Multiplier4;
    }

    if (multiple == 9) {
        this.gameObject.GetComponent<SpriteRenderer> ().sprite = Multiplier5;
    }

    if (multiple == 10) {
        this.gameObject.GetComponent<SpriteRenderer> ().sprite = Multiplier6;
    }

    if (multiple == 15) {
        this.gameObject.GetComponent<SpriteRenderer> ().sprite = Multiplier7;
    }

    if (multiple == 25) {
        this.gameObject.GetComponent<SpriteRenderer> ().sprite = Multiplier8;
    }

}

}