An error is displayed when a user without permissions attempts to view a discussion in a forum.

Replication steps:

1. Log in as admin
2. Navigate to a course
3. Edit the settings of the course and allow guest access
4. Create a forum or use a course's News forum
5. Create a post in the forum if there is not already one there
6. While viewing the forum, in the Settings block under Forum administration, click Permissions
7. Locate the permission "View discussions" and click the X next to Guest
8. Log into the course as a Guest
9. Go to the forum and attempt to view the discussion
10. Note message displayed "You do not have the permission to view discussions in this forum"
11. Click "continue" and the following error is shown.

Parameter missing

More information about this error

Debug info: 

Error code: missingparameter

Stack trace:

line 467 of \lib\setuplib.php: moodle_exception thrown

line 86 of \mod\forum\view.php: call to print_error()