NullReferenceException: Object reference not set to an instance of an object

hi guys, i am totally new in unity 3D and i am following this tutorial http://youtu.be/HzTceINFowY?t=15m47s, but the guy uses javaScript and i have some c backgraund and i want use c# instead(i've never programed in c# before)

unity3D give me this error

 NullReferenceException: Object reference not set to an instance of an object
 UnityEditor.AddComponentWindow.get_className () (at C:/BuildAgent/work/7535de4ca26c26ac/Editor/Mono/Inspector/AddComponentWindow.cs:300)
 UnityEditor.AddComponentWindow+NewScriptElement.OnGUI () (at C:/BuildAgent/work/7535de4ca26c26ac/Editor/Mono/Inspector/AddComponentWindow.cs:97)
 UnityEditor.AddComponentWindow.ListGUI (.Element[] tree, Single anim, UnityEditor.GroupElement parent, UnityEditor.GroupElement grandParent) (at C:/BuildAgent/work/7535de4ca26c26ac/Editor/Mono/Inspector/AddComponentWindow.cs:756)
 UnityEditor.AddComponentWindow.OnGUI () (at C:/BuildAgent/work/7535de4ca26c26ac/Editor/Mono/Inspector/AddComponentWindow.cs:525)
 System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Applications/buildAgent/work/84669f285f6a667f/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)
 Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.
 System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Applications/buildAgent/work/84669f285f6a667f/mcs/class/corlib/System.Reflection/MonoMethod.cs:232)
 System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) (at /Applications/buildAgent/work/84669f285f6a667f/mcs/class/corlib/System.Reflection/MethodBase.cs:115)
 UnityEditor.HostView.Invoke (System.String methodName, System.Object obj) (at C:/BuildAgent/work/7535de4ca26c26ac/Editor/Mono/GUI/DockArea.cs:234)
 UnityEditor.HostView.Invoke (System.String methodName) (at C:/BuildAgent/work/7535de4ca26c26ac/Editor/Mono/GUI/DockArea.cs:227)
 UnityEditor.HostView.OnGUI () (at C:/BuildAgent/work/7535de4ca26c26ac/Editor/Mono/GUI/DockArea.cs:120)

here is the code using UnityEngine; using System.Collections;

 public class MeleeSystem : MonoBehaviour 
 {
     
     public int TheDamage = 50;
     public float Distance;
 
     /*// Use this for initialization
     void Start () {
     
     }*/
     
     // Update is called once per frame
     void Update () 
     {
         
         Vector3 fwd = transform.forward; //transform.TransformDirection(Vector3.forward)
         RaycastHit hit;
         
         
         if (Input.GetButtonDown("Fire1")) 
         {
         //RaycastHit hit = new RaycastHit();
         
         
         //if (Physics.Raycast(transform.position, transform.InverseTransformDirection(Vector3.forward), hit) ) {
          if (Physics.Raycast(transform.position, fwd,out hit)) 
          {
             Distance = hit.distance;
             hit.transform.SendMessage("ApplyDamage", TheDamage, SendMessageOptions.DontRequireReceiver);
          }
             
        }
    }            
 }
 
 

thanks.