Steps to reproduce

1. Create a course or go to an existing one
2. Add a "custom reports" block
3. Click "Manage reports"
4. In the "Import report from repository" section, in the "Category" drop-down list, switch the category from "..." to any other the following actions must be performed quickly switch the category back to "..." and in the "Report" drop-down list, select a report named README (if there is no such a report, repeat step 4)
5. We get an error and click "continue"
6. In the "Import report from repository" section, in the "Category" drop-down list, switch the category from "..." to any other the following actions must be performed quickly switch the category back to "..." and in the "Report" drop-down list, select any report named undefined (if there is no such a report, repeat step 6)

The result

error/errorimporting

Debug info:
Error code: errorimporting
$a contents:
Stacktrace:

   line 70 of /blocks/configurable_reports/managereport.php: moodle_exception thrown

Output buffer: <br /> <b>Notice</b>: Trying to get property 'content' of non-object in <b>[path_to_moodle]/blocks/configurable_reports/managereport.php</b> on line <b>59</b><br />

After getting the error, the drop-down lists in the "Import report from repository" section will be empty. Clearing the cache / incognito mode / restarting the browser do not help. Only after about an hour will the elements appear in the drop-down lists again.

Expected result

No errors. Drop-down lists in the "Import report from repository" show the reports.