I have made a class including variables in Monodevelop which is:

public class GridInfo : MonoBehaviour {

    public float initPosX;
    public float initPosY;
    public bool inUse;
    public int f;
    public int g;
    public int h;
    public GridInfo parent;
    public int  y,x;        
}

Now I am using its class variable in another class, Map.cs which is:

public class Map : MonoBehaviour {

    public static GridInfo[,] Tile = new GridInfo[17, 23];

    void Start() {

        Tile[0,0].initPosX = initPosX;  //Line 49
    }
}

I am not getting any error on runtime, but when I play in unity it is giving me error

NullReferenceException: Object reference not set to an instance of an object
Map.Start () (at Assets/Scripts/Map.cs:49)

I am not inserting this script in any gameobject, as Map.cs will make a GridInfo type array, I have also tried using variables using GetComponent, where is the problem ?