NullReferenceException when using GetComponent for adding stats.

I am using the Survival Shooter tutorial code and i am trying to prototype upgrading damage.

This is the code for PlayerShooting

using UnityEngine;
using UnitySampleAssets.CrossPlatformInput;

namespace CompleteProject
{
    public class PlayerShooting : MonoBehaviour
    {
        public int damagePerShot = 20;                  // The damage inflicted by each bullet.
        public float timeBetweenBullets = 0.15f;        // The time between each shot.
        public float range = 100f;                      // The distance the gun can fire.


        float timer;                                    // A timer to determine when to fire.
        Ray shootRay = new Ray();                       // A ray from the gun end forwards.
        RaycastHit shootHit;                            // A raycast hit to get information about what was hit.
        int shootableMask;                              // A layer mask so the raycast only hits things on the shootable layer.
        ParticleSystem gunParticles;                    // Reference to the particle system.
        LineRenderer gunLine;                           // Reference to the line renderer.
        AudioSource gunAudio;                           // Reference to the audio source.
        Light gunLight;                                 // Reference to the light component.
		public Light faceLight;								// Duh
        float effectsDisplayTime = 0.2f;                // The proportion of the timeBetweenBullets that the effects will display for.


        void Awake ()
        {
            // Create a layer mask for the Shootable layer.
            shootableMask = LayerMask.GetMask ("Shootable");

            // Set up the references.
            gunParticles = GetComponent<ParticleSystem> ();
            gunLine = GetComponent <LineRenderer> ();
            gunAudio = GetComponent<AudioSource> ();
            gunLight = GetComponent<Light> ();
			//faceLight = GetComponentInChildren<Light> ();
        }


        void Update ()
        {
            // Add the time since Update was last called to the timer.
            timer += Time.deltaTime;

#if !MOBILE_INPUT
            // If the Fire1 button is being press and it's time to fire...
			if(Input.GetButton ("Fire1") && timer >= timeBetweenBullets && Time.timeScale != 0)
            {
                // ... shoot the gun.
                Shoot ();
            }
#else
            // If there is input on the shoot direction stick and it's time to fire...
            if ((CrossPlatformInputManager.GetAxisRaw("Mouse X") != 0 || CrossPlatformInputManager.GetAxisRaw("Mouse Y") != 0) && timer >= timeBetweenBullets)
            {
                // ... shoot the gun
                Shoot();
            }
#endif
            // If the timer has exceeded the proportion of timeBetweenBullets that the effects should be displayed for...
            if(timer >= timeBetweenBullets * effectsDisplayTime)
            {
                // ... disable the effects.
                DisableEffects ();
            }
        }


        public void DisableEffects ()
        {
            // Disable the line renderer and the light.
            gunLine.enabled = false;
			faceLight.enabled = false;
            gunLight.enabled = false;
        }


        void Shoot ()
        {
            // Reset the timer.
            timer = 0f;

            // Play the gun shot audioclip.
            gunAudio.Play ();

            // Enable the lights.
            gunLight.enabled = true;
			faceLight.enabled = true;

            // Stop the particles from playing if they were, then start the particles.
            gunParticles.Stop ();
            gunParticles.Play ();

            // Enable the line renderer and set it's first position to be the end of the gun.
            gunLine.enabled = true;
            gunLine.SetPosition (0, transform.position);

            // Set the shootRay so that it starts at the end of the gun and points forward from the barrel.
            shootRay.origin = transform.position;
            shootRay.direction = transform.forward;

            // Perform the raycast against gameobjects on the shootable layer and if it hits something...
            if(Physics.Raycast (shootRay, out shootHit, range, shootableMask))
            {
                // Try and find an EnemyHealth script on the gameobject hit.
                EnemyHealth enemyHealth = shootHit.collider.GetComponent <EnemyHealth> ();

                // If the EnemyHealth component exist...
                if(enemyHealth != null)
                {
                    // ... the enemy should take damage.
                    enemyHealth.TakeDamage (damagePerShot, shootHit.point);
                }

                // Set the second position of the line renderer to the point the raycast hit.
                gunLine.SetPosition (1, shootHit.point);
            }
            // If the raycast didn't hit anything on the shootable layer...
            else
            {
                // ... set the second position of the line renderer to the fullest extent of the gun's range.
                gunLine.SetPosition (1, shootRay.origin + shootRay.direction * range);
            }
        }
    }
}

And this is my ‘DamageUpgrade’ Script:

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

public class DamageUpgrade : MonoBehaviour {

    public float multiplier = 1.2f;

	// Use this for initialization
	void Start () {
        
	}
	
	// Update is called once per frame
	void Update () {


        if (Input.GetKeyDown(KeyCode.U))

            UpDamage();

            




	}


    void UpDamage()
    {
        Debug.Log("Damage Up?");
        PlayerShooting weaponDamage = GetComponent<PlayerShooting>();
        weaponDamage.damagePerShot *= (int)multiplier;

    }
}

When I press U the game pauses and gives me the error.

The PlayerShooting Script is on the GunBarrel which is a child to the player.
I Have put the DamageUpgrade Script onto the Player which is Parent to the GunBarrel.

What exactly is the error message? The error message usually contains the name of the script and the line number where the error occurs. This is the first thing to look at.