get a sum from a sql table using linq to sql visual studio 2008 c#

I am trying to sum a field in a table.  If I use this method:

                        decimal? TotHrs2 = (from i in dc2.esna_JobAnalysis
                                   where i.emp_no == Emp.EmployeeId &&
                                   i.work_date == dt
                                   select i.hours).Sum();

I get this error:

"The null value cannot be assigned to a member with type System.Decimal which is a non-nullable value type."

This, of course works:

                        var GetHours = from i in dc.esna_JobAnalysis
                                                        where i.emp_no == Emp.EmployeeId &&
                                                        i.work_date == dt
                                                        select new { i.hours };

                        decimal TotHrs1 = 0;
                        foreach (var GH in GetHours)
                        {
                            TotHrs1 += GH.hours;
                        }

However, I'm hoping to avoid the loop.  Can't this be done with a .Sum using linq?  What am I doing wrong in the first example?

Thank you!