Hi Hennig,

while testing your plugin for the latest Moodle release we've encountered the problem that the "Export to portfolio" link throws a file not found error.

Steps to reproduce

Prerequisites:

1. Enrol a teacher into a course
2. Enable portfolios in the instance: enableportfolios set to yes
3. Manage portfolios (admin/portfolio.php): Set "File download" to Enabled and visible

1. Login as the teacher
2. Go to the course
3. Turn editing mode on
4. Add an assignment
5. Enable "Solution Sheet" and upload a document
6. Save and display
7. See that there's a plus icon with the hover text "Export to portfolio" behind the solution sheet file
8. Click that button
9. Get the error "Sorry, the requested file could not be found More information about this error"

(With debugging on you'll that these further information:

Debug info:

Error code: filenotfound

Stack trace:

line 9394 of /mod/assign/locallib.php: portfolio_caller_exception thrown

line 185 of /portfolio/add.php: call to assign_portfolio_caller->load_data()

)

We've seen that this bug occurs in Moodle 3.6+, too.

Best, Kathrin