mod_assign_get_grades doesnt return optional value

Hello, I am testing to get student grades using mod_assign_get_grades service.
I have managed to get the assignment results but the "gradefordisplay" field does not show it.

At first I thought that there was no showing it because of a permission issue.
I then tried the gradereport_user_get_grade_items service and that way I was able to get the "gradeformatted".

I got to see the mod_assign_get_grades service source code and couldn't find it referring to the optional field.

Could it be missing including it in the service?

Thanks in advance.