Hi whenever i am trying to add cart . I am getting following error.

Error:

Object reference not set to an instance of an object.

public Entry Entry { get; set; }

public Func<Entry, bool> FilterAction { get; set; }
protected void Page_Load(object sender, EventArgs e)
{
// getcart();
}

protected void btnBuy_Click(object sender, EventArgs e)
{
CartHelper test = new CartHelper(Cart.DefaultName);

if (Entry != null)
{
Entry entry = Entry;

if (FilterAction != null)
{
entry = Entry.Entries.Entry.FirstOrDefault(FilterAction);
test.AddEntry(entry);
}

}

}

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an object.]
   Mediachase.Commerce.Website.Helpers.CartHelper.CreateLineItem(Entry entry, Decimal quantity, String warehouseCode) +853
   Mediachase.Commerce.Website.Helpers.CartHelper.AddEntry(Entry entry, Decimal quantity, Boolean fixedQuantity, String warehouseCode, CartHelper[] helpersToRemove) +718
   Mediachase.Commerce.Website.Helpers.CartHelper.AddEntry(Entry entry, Decimal quantity, Boolean fixedQuantity, CartHelper[] helpersToRemove) +79
   Mediachase.Commerce.Website.Helpers.CartHelper.AddEntry(Entry entry) +143
   DemoTest.Sample.Units.ProductDetail.SharedModule.AddToCart.btnBuy_Click(Object sender, EventArgs e) in C:\EPiServer\DemoVisualStudioCTP17\wwwroot\Sample\Units\ProductDetail\SharedModule\AddToCart.ascx.cs:43
   System.Web.UI.WebControls.LinkButton.OnClick(EventArgs e) +116
   System.Web.UI.WebControls.LinkButton.RaisePostBackEvent(String eventArgument) +101
   System.Web.UI.WebControls.LinkButton.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +9642610
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1724

I am geeting Entry properly. but I am not able to find the attribute which i am missing. 

can anyone suggest me ? Which thing i am missing over here ?

Thanks in advance.

regards,
Paragi