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>This way you do not have to think of if the underlying field r.Weight is nullable or not. Otherwise it would not only depend on underlying field is nullable or not but if there are matching records to sum as well.
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>PS: I removed the parentheses just because they were not needed.

So you're saying I should treat the details table as well for empty queries and I see your point. I'm not sure I'm breaking some best practices rule here, but I have reasons to believe that there will always be entries in the details table and if not, the code is welcome to break. (ducks).