Implementation of "Method 2: Random node in the whole graph"

I am trying to implement the Wandering AI Tutorial.
The “Method 1: Random point inside a circle” works simply using the script available within the additional tutorials.
Now I am trying to implement the “Method 2: Random node in the whole graph” but it does not work. The following definition within a Start() gives me an error:
List nodes = new List()
Please note that I am using a Recast Graph.
How can I fix it?
Thanks in advance!

I cannot understand because the line “List nodes = new List();” in the following script gives me an error. What’s wrong with it? Anyone could help me?

using UnityEngine;
using System.Collections;
using Pathfinding;

public class WanderingDestinationSetter_InsideGraph : MonoBehaviour
IAstarAI ai;

float x;
public float RandomInitialXmin = -50;
public float RandomInitialXmax = 50;

public float RandomInitialY = 20;

float z;
public float RandomInitialZmin = -50;
public float RandomInitialZmax = 50;

public GameObject Obstacle;

Vector3 pos;

GraphNode randomNode;

void Start()
    ai = GetComponent<IAstarAI>();

    //Set a random initial position
    x = Random.Range(RandomInitialXmin, RandomInitialXmax);
    //y = 2;
    z = Random.Range(RandomInitialZmin, RandomInitialZmax);
    pos = new Vector3(x, RandomInitialY, z);
    transform.position = pos;

    // Works for ANY graph type, however this is much slower
    var graph =[0];
    // Add all nodes in the graph to a list

    List<GraphNode> nodes = new List<GraphNode>(); //HERE THE ERROR, HOW CAN I FIX IT?

    randomNode = nodes[Random.Range(0, nodes.Count)];

Vector3 PickRandomPoint()
    // Use a random point on the surface of the node as the destination.
    // This is useful for navmesh-based graphs where the nodes are large.
    var point = randomNode.RandomPointOnSurface();

    return point;

void FixedUpdate()
    // Update the destination of the AI if
    // the AI is not already calculating a path and
    // the ai has reached the end of the path or it has no path at all
    if (!ai.pathPending && (ai.reachedEndOfPath || !ai.hasPath || velz == 0))
        ai.destination = PickRandomPoint();



I think you also need to include the line

using System.Collections.Genetic;

as that’s where the List class lives.