public static decimal ComputeWeightDifference(int transactionHeaders_Id,PICSEntities context)
        {
            decimal emWeight = (decimal) context.EMTransactions.Where(r => (r.TransactionHeaders_Id == transactionHeaders_Id)).Sum(r => r.Weight) ?? 0;
            decimal? detailsWeight = 0;
            emWeight = (decimal?) context.EMTransactions.Where(r => (r.TransactionHeaders_Id == transactionHeaders_Id)).Sum(r => r.Weight) ?? 0;
            detailsWeight = context.TransactionDetails.Where(r => (r.TransactionHeaders_Id == transactionHeaders_Id)).Sum(r => r.Weight);
            return (decimal)(emWeight  - (decimal) (detailsWeight ?? 0);
        }

I'm really puzzled by this statement:

          decimal emWeight = context.EMTransactions.Where(r => (r.TransactionHeaders_Id == transactionHeaders_Id)).Sum(r => r.Weight) ?? 0;

It won't compile. CS0019 Operator '??' cannot be applied to operands of type 'decimal' and 'int'

But this does :

return emWeight  - (decimal) (detailsWeight ?? 0);

So is there a way to do is in one line, or do I first need to extract the transactions and check if there are none?