RA session timeout leads to fatal error

[thijskh]

When your RA (6.1.0) session times out a type error on the return of getCurrentRequestUri() is generated.

Reproduce

1. Log in as a user to the RA portal
2. Let the session time out
3. Click something in the RA portal / reload it
4. Be presented with "Internal server error" Symfony screen

Logging shows:

{"message":"Uncaught PHP Exception TypeError: \"Surfnet\\StepupRa\\RaBundle\\Security\\Authentication\\Session\\SessionStorage::getCurrentRequestUri(): Return value must be of type string, null returned\" at SessionStorage.php line 94","context":{"exception":{"class":"TypeError","message":"Surfnet\\StepupRa\\RaBundle\\Security\\Authentication\\Session\\SessionStorage::getCurrentRequestUri(): Return value must be of type string, null returned","code":0,"file":"/var/www/html/src/Surfnet/StepupRa/RaBundle/Security/Authentication/Session/SessionStorage.php:94"}},"level":500,"level_name":"CRITICAL"}