Keeping ViewState in SessionPageStatePersister

I want to keep viewstate of a specific page in session but following code block does not help me, what might I be missing?

So here is the code-behind file content of my page;

    public partial class ConfigurationEditorWebForm : PageBase
    {
        protected void Page_Load(object sender, EventArgs e)
        {
        }

        protected override bool VerifyAccess()
        {
            return true;
        }

        protected override PageStatePersister PageStatePersister
        {
            get
            {
                return new SessionPageStatePersister(this);
            }
        }
    }