Unity:Integer returning Null when called

Question

I'm trying to build a game with the help of the following unity tutorial , in the code currentHealth is called from EnemyHealth in EnemyAttack and EnemyMovement.while referring to tutorial 7 did everything as mentioned but getting NullReferenceException errors in EnemyMovement.cs:2 and EnemyAttack.cs:58. I have already checked if I have accidentally assigned the script to other game object,but its not.

EnemyHealth

    public class EnemyHealth : MonoBehaviour
{
    public int startingHealth = 100;
    public int currentHealth;
    public float sinkSpeed = 2.5f;
    public int scoreValue = 10;
    public AudioClip deathClip;
    Animator anim;
    AudioSource enemyAudio;
    ParticleSystem hitParticles;
    CapsuleCollider capsuleCollider;
    bool isDead;
    bool isSinking;

    void Awake ()
    {
        anim = GetComponent <Animator> ();
        enemyAudio = GetComponent <AudioSource> ();
        hitParticles = GetComponentInChildren <ParticleSystem> ();
        capsuleCollider = GetComponent <CapsuleCollider> ();

        currentHealth = startingHealth;
    }

    void Update ()
    {
        if(isSinking)
        {
            transform.Translate (-Vector3.up * sinkSpeed * Time.deltaTime);
        }
    }

    public void TakeDamage (int amount, Vector3 hitPoint)
    {
        if(isDead)
            return;

        enemyAudio.Play ();

        currentHealth -= amount;

        hitParticles.transform.position = hitPoint;
        hitParticles.Play();

        if(currentHealth <= 0)
        {
            Death ();
        }
    }

    void Death ()
    {
        isDead = true;

        capsuleCollider.isTrigger = true;

        anim.SetTrigger ("Dead");

        enemyAudio.clip = deathClip;
        enemyAudio.Play ();
    }

    public void StartSinking ()
    {
        GetComponent <NavMeshAgent> ().enabled = false;
        GetComponent <Rigidbody> ().isKinematic = true;
        isSinking = true;
        //ScoreManager.score += scoreValue;
        Destroy (gameObject, 2f);
    }
}

EnemyAttack

    public class EnemyAttack : MonoBehaviour
    {
        public float timeBetweenAttacks = 0.5f;     // The time in seconds between each attack.
        public int attackDamage = 10;               // The amount of health taken away per attack.


        Animator anim;                              // Reference to the animator component.
        GameObject player;                          // Reference to the player GameObject.
        PlayerHealth playerHealth;                  // Reference to the player's health.
        EnemyHealth enemyHealth;                    // Reference to this enemy's health.
        bool playerInRange;                         // Whether player is within the trigger collider and can be attacked.
        float timer;                                // Timer for counting up to the next attack.


        void Awake ()
        {
            // Setting up the references.
            player = GameObject.FindGameObjectWithTag ("Player");
            playerHealth = player.GetComponent <PlayerHealth> ();
            enemyHealth = GetComponent<EnemyHealth>();
            anim = GetComponent <Animator> ();
        }


        void OnTriggerEnter (Collider other)
        {
            // If the entering collider is the player...
            if(other.gameObject == player)
            {
                // ... the player is in range.
                playerInRange = true;
            }
        }


        void OnTriggerExit (Collider other)
        {
            // If the exiting collider is the player...
            if(other.gameObject == player)
            {
                // ... the player is no longer in range.
                playerInRange = false;
            }
        }


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

            // If the timer exceeds the time between attacks, the player is in range and this enemy is alive...
            if(timer >= timeBetweenAttacks && playerInRange && enemyHealth.currentHealth > 0)
            {
                // ... attack.
                Attack ();
            }

            // If the player has zero or less health...
            if(playerHealth.currentHealth <= 0)
            {
                // ... tell the animator the player is dead.
                anim.SetTrigger ("PlayerDead");
            }
        }


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

            // If the player has health to lose...
            if(playerHealth.currentHealth > 0)
            {
                // ... damage the player.
                playerHealth.TakeDamage (attackDamage);
            }
        }
    }
}

EnemyMovement

public class EnemyMovement : MonoBehaviour
{
    Transform player;               // Reference to the player's position.
    PlayerHealth playerHealth;      // Reference to the player's health.
    EnemyHealth enemyHealth;        // Reference to this enemy's health.
    NavMeshAgent nav;               // Reference to the nav mesh agent.


    void Awake ()
    {
        // Set up the references.
        player = GameObject.FindGameObjectWithTag ("Player").transform;
        playerHealth = player.GetComponent<PlayerHealth>();
        enemyHealth = GetComponent <EnemyHealth> ();
        nav = GetComponent <NavMeshAgent> ();
    }


    void Update ()
    {
        // If the enemy and the player have health left...
        if(enemyHealth.currentHealth > 0 && playerHealth.currentHealth > 0)
        {
            // ... set the destination of the nav mesh agent to the player.
            nav.SetDestination (player.position);
        }
        // Otherwise...
        else
        {
            // ... disable the nav mesh agent.
            nav.enabled = false;
        }
    }
}