c# - Value cannot be null. Error -

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i have error method below trying add data combobox datagrid , after add data want calculate total amount of 'itemsellingprice' , display amount in label.

using (truckserviceclient tsc = new truckserviceclient()) {     var item = cmbaddextras.selecteditem extradisplayitems;      if (item != null)     {         var displayitem = new list<extradisplayitems>         {             new extradisplayitems              {                  displayitems = item.displayitems,                 itemid = item.itemid,                  itemcode = item.itemcode,                  itemdescription = item.itemdescription,                  itemsellingprice = item.itemsellingprice,             }         };         dgaddextras.items.add(item);         var subtotalextras = item.displayitems.sum(x => x.itemsellingprice.getvalueordefault(0)); //here         lblsubtotalextrasamount.content = "r" + subtotalextras;     } }

the error is:

value cannot null.

does have ideas why happening?

edit: set displayitems in class

public class extradisplayitems {     public list<extradisplayitems> displayitems;      public int itemid { get; set; }         public string itemcode { get; set; }         public string itemdescription { get; set; }         public double? itemsellingprice { get; set; } }

thanks gert arnold, actual issue item.displayitems null (so not inside lambda, since works fine).

some proof. gets exact error message:

double?[] x = null; double? sum = x.sum(y => y);

(the reason don't nullreferenceexception call static method (an extension method), technically reference isn't null argument is).

you should check set item.displayitems or prevent calling sum on item.displayitems value null.


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