private decimal replaceNullZero(decimal dec)
{
   if (dec == null)
   {
     return 0;
   }
     else
   {
     return dec;
   }
}

public decimal MyProperty
{
   get 
   {
       if (dr["MyProperty"] == null)
           return 0
       return (decimal)dr["MyProperty"]
   } 
}

Actually used this code:

                    decimal dADLeaseHold = 0;
                    decimal dADComm = 0;
                    decimal dADFurn = 0;
                    if (mepExpenseSummary.ADLeaseHold.HasValue)
                    {
                        dADLeaseHold = (decimal)mepExpenseSummary.ADLeaseHold;
                    }
                    if (mepExpenseSummary.ADComm.HasValue)
                    {
                        dADComm = (decimal)mepExpenseSummary.ADComm;
                    }
                    if (mepExpenseSummary.ADFurn.HasValue)
                    {
                        dADFurn = (decimal)mepExpenseSummary.ADFurn;
                    }

                    decimal aggregate = (decimal)mepExpenseRep.continuedad + 
                        (decimal)mepExpenseRep.sum_annualoccupancy + 
                        (decimal)mepExpenseSummary.CapExpensedItems +
                        dADLeaseHold + 
                        dADComm + 
                        dADFurn;

We check for null in many-many places, but probably not in all. Some derived fields will always have values and it is handled in sproc, etc.