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 "Categories" 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, sel ect any report named README
5. We get an error and click "continue"
   Then repeat the following steps until we get another error: switch the report category fr om "..." to any other, periodically opening the "Report" drop-down list, and do this several times until the page itself refreshes and we get a new error that is different from the error from step 4.
   If you cannot get an error for a long time, then do everything from step 4.

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>Warning</b>: Attempt to read property "content" on null in <b>[path_to_moodle]/blocks/configurable_reports/managereport.php</b> on line <b>59</b><br /> <br /> <b>Deprecated</b>: base64_decode(): Passing null to parameter #1 ($string) of type string is deprecated in <b>[path_to_moodle]/blocks/configurable_reports/managereport.php</b> on line <b>59</b><br /> +

Expected result

No errors