For loop throwing NullReferenceException ( reading in XML file from API )

Would anyone have any idea as to why this code is throwing a NullReferenceException? Basically what it does is when I click a Search button it executes this method which grabs some stuff from an API and puts into a Object and those Objects into a List.

private List<Show> _shows;
    public List<Show> Shows
    {
        get
        {
            return _shows;
        }
        set
        {
            _shows = value;
        }
    }

    public void Search(string query)
    {
        List<Show> lijst = new List<Show>();
        XmlDocument doc = new XmlDocument();
        doc.Load(baseUrl + "/api/GetSeries.php?seriesname=" + query);
        XmlNodeList elemList = doc.GetElementsByTagName("Series");

        for(int i=0; i < elemList.Count; i++)
        {
            XmlNode elem = elemList[i];
            Uri banner = new Uri("http://ift.tt/1fx5B65" + elem["banner"].InnerText); 
            Show sh = new Show()
            {
                Name = elem["SeriesName"].InnerText,
                Banner = banner,
                Overview = elem["Overview"].InnerText,
                FirstAired = Convert.ToDateTime(elem["FirstAired"].InnerText),
            };
            lijst.Add(sh);
        }

        this._shows = lijst;
    }

I'm quite the beginner when it comes to this stuff so I might be overlooking something really obvious. Thanks in advance anyways.