Section 7.2, Examples 50: aggregate returns one item even for empty input set

Example 50 shows an empty collection value for the Sales navigation property in the third item, but according to the definition of aggregate() it will return a single instance even if the input set is empty. And according to the definition of aggregation method sum the sum over no values is null, hence the Sales navigation property will contain one item with a Total of null.

The important point is that the group for product "Pencil" exists because the aggregation base set is the Products entity set, not the Sales entity set.