why do i get System.NullReferenceException:?

Question

I am trying to add an object to a list of objects in c#, and i get an System.NullReferenceException: Can someone figure out why?

This is the code;

   public List<PodcastShow> Podcasts { get; set; }

    public BLL()
    {

        Podcasts = new List<PodcastShow>();
        Categories = new List<Category>();
        rssR = new RSSreader();
    } //contructor

    public void newPodcast(string url, string category, string frequency)
    {
        PodcastShow newPod = new PodcastShow(url, category, frequency);
       addToPodcastList(newPod);


    }

    private void addToPodcastList(PodcastShow newPod)
    {  

            Podcasts.Add(newPod); <--- this is the place i get the nullrefrence exeption is thrown
    }

i do instanciate BLL in a form

public Form1()
    {
        InitializeComponent();
        timer1.Start();
        timer2.Start();
        timer3.Start();
        bll = new BLL();
        WebClient client = new WebClient();
        bll.getPodcastShos();
        FillLvPodcast();
        PopulateCategoryList();
    }

This is the button wich calls on the newPodcast method:

                    string url = txtURL.Text;
                string cat = cboKategori.Text;
                string updtF = cboUppdateringsfrekverns.Text.ToString();

                bll.newPodcast(url, cat, updtF);
                ListViewItem podcastItem = new ListViewItem(bll.getPodcastTitleUrl(txtURL.Text));
                podcastItem.SubItems.Add(cboUppdateringsfrekverns.Text);

                podcastItem.SubItems.Add(cboKategori.Text);
                var counter = bll.podCastEpCounter(bll.getPodcastTitleUrl(txtURL.Text));
                lvPodcast.Items.Add(podcastItem);
                lvEpisodes.Items.Add(counter.ToString());
                bll.serializePodcastShow();

this is the exception i get System.NullReferenceException: Object reference not set to an instance of an object.

Logic.BLL.Podcasts.get returned null.