Summary: When "Aggregate only non-empty grades" is NOT selected for a gradebook category, according to Moodle doc, that category total should display zeroes. However, the category total is showing "dashes" just as if "Aggregate only non-empty grades" WAS selected.

1. Create a category, set to Weighted Mean of Grades, select "Aggregate only non-empty grades".
2. Create two more categories, set to Mean of grades, DO NOT select "Aggregate only non-empty grades". Make these categories a sub-category of the first category you created.
3. Create a couple of assignments for each of these sub-categories.
4. Enroll a student and review the User Report for this student.
According to the Moodle doc, the two subcategories created should be displaying a zero for the student category grades. However, only "dashes" are appearing. (Moodle doc: (http://docs.moodle.org/23/en/Grade_categories#Aggregate_only_non-empty_grades)
5. If you add grades for this student for any of the displayed assignments, then remove the grade, the category total will correctly display a zero (or "F").
The Gradebook should be treating the empty grade items as zeros and calculating the total with appropriate aggregation and displaying the proper total.