There is an error message displayed when editing a new or existing forum's configuration.

Replication steps:

1. Log in as teacher/admin
2. Navigate to a course
3. Edit an existing forum or create a new one

Expected result: No errors shown

Actual result: The following error message is displayed at the top of the form.

I've noted this in a number of other activities also.

Notice: Undefined property: core_string_manager::$usediskcache in D:\xampp\htdocs\moodle_master_test_postgreSQL\lib\moodlelib.php on line 7033