MDL-74610 introduced gradeitemmarks in the mod_quiz_get_attempt_review Web Service response, but it doesn't seem to be consistent with sumgrades.

Before grading, which is displayed to users as "Not yet graded", the sumgrades property is null. Once grading has been completed, this property has a numeric value (0, for example). But the gradeitemmarks.grade property always has a numeric value, so clients can't discern whether grading has been completed or not for the grade item marks. They can work around it by looking at the value of sumgrades, and assume it will be the same for the grade item marks. But it'd be better to have a consistent behaviour.