While playing with Oracle I get:

ORA-01407: cannot update ("STRONK7_19"."M_GRADE_CATEGORIES"."KEEPHIGH") to NULL

UPDATE m_grade_categories SET courseid = '21',parent = NULL,depth = '1',path = '/4/',fullname = '?',aggregation = '11',keephigh = '',droplow = '0',aggregateonlygraded = '1',aggregateoutcomes = '1',aggregatesubcats = '1',timecreated = '1206208578',timemodified = '1206231472' WHERE id = 4

• line 1704 of lib/dmllib.php: call to debugging()
• line 205 of lib/grade/grade_object.php: call to update_record()
• line 222 of lib/grade/grade_category.php: call to grade_object->update()
• line 877 of lib/grade/grade_category.php: call to grade_category->update()
• line 784 of lib/grade/grade_category.php: call to grade_category->get_children()
• line 1299 of grade/lib.php: call to grade_category->fetch_course_tree()
• line 122 of grade/report/grader/lib.php: call to grade_tree->grade_tree()
• line 122 of grade/report/grader/index.php: call to grade_report_grader->grade_report_grader()

Problem seems to be the "keephigh" field whose value, when inserted, is '' (empty string). Tracing the problem down, I've found that the grade_category->apply_forced_settings() call changes the previous value of "keephigh" from 0 to empty string and is the final cause for breakage.

Code in apply_forced_settings() seems to rely on $CFG->grade_keephigh, that, in my server is empty string.

To reproduce, I just installed 1.9 under Oracle, created one course and press in the gradebook. Then the error above happened (and some sort of infinite recursion killing the web server).

Ciao