Draw line errors

Hello,

I have a question about drawing lines dynamically. The thing is that I found a tutorial with a sample code, but I cannot make it, asked there but the last answered question is 4 months ago so I am looking here for help. So, this is the code:

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class DrawLine : MonoBehaviour 
 {
     private LineRenderer line;
     private bool isMousePressed;
     private List<Vector3> pointsList;
     private Vector3 mousePos;
 
     // Structure for line points
     struct myLine
     {
         public Vector3 StartPoint;
         public Vector3 EndPoint;
     };
     //    -----------------------------------    
     void Start()
     {
         // Create line renderer component and set its property
         line = gameObject.AddComponent<LineRenderer>();
         line.material =  new Material(Shader.Find("Particles/Additive"));
         line.SetVertexCount(0);
         line.SetWidth(0.1f,0.1f);
         line.SetColors(Color.green, Color.green);
         line.useWorldSpace = true;    
         isMousePressed = false;
         pointsList = new List<Vector3>();
 //        renderer.material.SetTextureOffset(
     }
     //    -----------------------------------    
     void Update () 
     {
         // If mouse button down, remove old line and set its color to green
         if(Input.GetMouseButtonDown(0))
         {
             isMousePressed = true;
             line.SetVertexCount(0);
             pointsList.RemoveRange(0,pointsList.Count);
             line.SetColors(Color.green, Color.green);
         }
         else if(Input.GetMouseButtonUp(0))
         {
             isMousePressed = false;
         }
         // Drawing line when mouse is moving(presses)
         if(isMousePressed)
         {
             mousePos = Camera.main.ScreenToWorldPoint(Input.mousePosition);
             mousePos.z=0;
             if (!pointsList.Contains (mousePos)) 
             {
                 pointsList.Add (mousePos);
                 line.SetVertexCount (pointsList.Count);
                 line.SetPosition (pointsList.Count - 1, (Vector3)pointsList [pointsList.Count - 1]);
                 
             }
         }
     }
     
 }

Can someone tell me what I am doing wrong? I create an empty object, add the script to the object and place a plane down with black texture.

This is the error I get and two warnings: NullReferenceException: Object reference not set to an instance of an object DrawLine.Awake () (at Assets/Scripts/DrawLine.cs:20)

Assets/Scripts/DrawLine.cs(6,30): warning CS0649: Field DrawLine.line' is never assigned to, and will always have its default value null' Assets/Scripts/DrawLine.cs(7,22): warning CS0414: The private field `DrawLine.isMousePressed' is assigned but its value is never used

This is the website where I found the code: http://www.theappguruz.com/tutorial/draw-line-mouse-move-detect-line-collision-unity2d-unity3d/