Project: moodle
Issue MDL-46599: Importing null grade data clears existing grades
If an instructor has a data file, that has null scores for students, and the instructor imports that file, any existing scores will be cleared with those null scores. *Example real-world scenario*: when there are large classes, with multiple graders, who only grade a subset of the students. Each grader may only enter scores for their students, and have nulls for all the others.
Story points: 40