LINQ isNull function

var result = from b in BillMain
             select new
             {
                 Qty =b.Qty ?? 0
             }

var orders =  from o in db.Orders select new {
    OrderID = o.OrderID == DBNull.Value ? 0 : o.OrderID, //Checking for null value and passing 0 if null
    o.CustomerID,
    o.EmployeeID,
    o.ShippedDate
}

YourContext db = new YourContext();

List<entity> list =  (from n in db.YourEntity
                     where n.FieldToCheck.Equals(null)
                     select n).ToList();

from c in dtx.Categories
where c.CategoryId == CatId
    && (string.IsNullOrEmpty(param1) || c.Param1 == param1)
    && (string.IsNullOrEmpty(param2) || c.Param2 == param2)
select c