When I save mod_form, I am getting
ERROR: null value in column "description" violates not-null constraint

INSERT INTO mdl_event ( ID, NAME, COURSEID, GROUPID, USERID, MODULENAME, INSTANCE, TIMEMODIFIED ) VALUES ( 25, 'Pokus', 2, 0, 0, 'certificate', 1, 1208895453 )

• line 1554 of lib/dmllib.php: call to debugging()
• line 5826 of lib/moodlelib.php: call to insert_record()
• line 136 of mod/certificate/lib.php: call to add_event()
• line 244 of course/modedit.php: call to certificate_update_instance()