Object reference not set to an instance of an object.

Question

Hello everyone and thanks in advance.
I am getting an error " Object reference not set to an instance of an object." when I try to add an item to a integer list of class "FreeHoursClass" which has a public list "FreeHoursList".

This is my code.

public class FreeHoursClass

    {

       public  List<int> FreeHoursList = new List<int>();

    }

private void button1_Click(object sender, EventArgs e)

        {

            FreeHoursClass[] ff = new FreeHoursClass[30];

            ff[5].FreeHoursList.Add(9);

            MessageBox.Show(ff[5].FreeHoursList[0].ToString());

        }