Question

public partial class MasterPages_Main : System.Web.UI.MasterPage
{
    public string TopMenuTab;
    public string SubMenuTab;
    public Configuration Config = WebConfigurationManager.OpenWebConfiguration(null);

    protected void Page_Load(object sender, EventArgs e)
    {
        ContentMenu.TopTabSelected = TopMenuTab;
        ContentMenu.SubTabSelected = SubMenuTab;

        Response.Write("K" + Config.AppSettings.Settings["BlogCommentsPerPage"].ToString());
    }

}

In web.config:

<appSettings>

    <!-- Website settings -->
    <add key="BlogCommentsPerPage" value="3" />

I get:

System.NullReferenceException: Object reference not set to an instance of an object.

On the response.write line

Answer 1

var commentsPerPage = ConfigurationSettings.AppSettings["BlogCommentsPerPage"];

do a null check and then call ToString() or Convert.ToInt32()