This is just a minor issue that I noticed while testing MDL-56948, in which the test involved removing a grade_items record. This exposed some bad code in mod/assign/locallib.

Basically, this line results in a notice if the gradebookgrade is null.

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if ((!is_null($gradebookgrade->grade) || !$emptyplugins)

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                && ($cangrade || !$gradebookgrade->hidden)) {

We need to check for a null object before trying to check the property.

To replicate is hard. In MDL-56948, some users indicated they were seeing errors because of missing grade_items records, however, we couldn't replicate this, so the testing instructions were to remove a record for the respective activity manually. Perhaps, in the past, Moodle didn't create grade_items for activities with Grade Type set to 'None', hard to say. In any case, you can see this error by:

1. Create an assignment
2. Manually delete the grade_items record for that assignment
3. View the assignment in debug mode
   Note: The notice will be hidden under the navbar if the theme is Boost.