Unable to delete users who have invalid course id in their grades

Recently we had issues with deleting users as it systematically throw an 'invalidrecord' error ("Can\'t find data record in database table {$a}.')

I tracked the issue down to the fact that the user was associated with grades items which are invalid (the course id is missing somewhat). 

The call stack looks like:

• the moodlelib.php: delete_user(4169)
• lib/gradelib.php: grade_user_delete (1529),
•  lib/grade/grade_grade.php: delete (1113)
• finally: lib/classes/event/grade_deleted.php (70)

So basically a exception is thrown when we create the event for the grade_deletion and then it "breaks" the deletion process altogether with a user which is not deleted.

My first thought was to catch the exception but I supose that's not the right way foward as the event will not be created. 

Any thought about if it is a problem that needs to be solved in the moodlelib/core moodle or there is a workaround somewhere ?

Seems that we have had a similar issue here #MDL-64895 on course deletion.