Impacted location: In web service administration: make service with authorized user, and add all functions. Add a student to the service. On the same page, missing capabilities are displayed for this student. No php error related to array_key_exists should be displayed. Run web services PHPunit test for /course/tests/externallib_tests.php, /enrol/tests/externallib_tests.php, /enrol/manual/tests/externallib_tests.php. go to the search page into the community block, check there is no php error related to array_key_exists. in the admin create a token for a student. Link the token to a service containing all functions. Some missing capabilities should be displayed in the page. Check there is no php error related to array_key_exists. trigger a moodle upgrade, check there is no error (a change has been done during web service functions update)