OU wiki: Should define capabilities used: error get_in_or_equal() does not accept empty arrays

moodle_database::get_in_or_equal() does not accept empty arrays

Stack trace:

line 595 of /lib/dml/moodle_database.php: coding_exception thrown
line 6410 of /lib/accesslib.php: call to moodle_database->get_in_or_equal()
line 7161 of /lib/accesslib.php: call to context_module->get_capabilities()
line 69 of /admin/roles/lib.php: call to fetch_context_capabilities()
line 261 of /admin/roles/lib.php: call to capability_table_base->__construct()
line 191 of /admin/roles/permissions.php: call to permissions_table->__construct()