Unable to fetch articles on new Android device

### Issue details

When I log in the Android app on a new device, it throws an error 500 when it try to fetch articles.
Other devices works fine. I checked wallabag_dir/var/logs/prod.log and these lines are added when i try to sync articles:

` -> request.INFO: Matched route "api_get_entries". {"route":"api_get_entries","route_parameters":{"_controller":"Wallabag\\ApiBundle\\Controller\\EntryRestController::getEntriesAction","_format":"json","_route":"api_get_entries"},"request_uri":"https://mywallabagdomain.tld/api/entries.json?order=asc&page=1&perPage=30&since=0&sort=created","method":"GET"} []
-> request.CRITICAL: Uncaught PHP Exception Doctrine\DBAL\Types\ConversionException: "Could not convert database value "a:1:{i:0;s:27:" ? V..." to Doctrine Type array" at /var/www/wallabag/vendor/doctrine/dbal/lib/Doctrine/DBAL/Types/ConversionException.php line 46 {"exception":"[object] (Doctrine\\DBAL\\Types\\ConversionException(code: 0): Could not convert database value \"a:1:{i:0;s:27:\" ? V...\" to Doctrine Type array at /var/www/wallabag/vendor/doctrine/dbal/lib/Doctrine/DBAL/Types/ConversionException.php:46)"} []
`

### Environment

* wallabag version : 2.3.8
* How did you install wallabag? `git clone`
* Last wallabag version that did not exhibit the issue (if applicable): 2.3.7
* php version: 7.2.24
* OS: Ubuntu Server 18.04 LTS
* type of hosting (shared or dedicated): dedicated
* which storage system you choose at install: MySQL

### Steps to reproduce/test case

1. Log in Android app for the first time
2. Launch sync operations