Exception: Nextcloud allows only integer log levels

[nenatap]

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Steps to reproduce

1. nextcloud:30.0.4-apache (docker version)
2. Upgraded preview generator via nextcloud apps menu to version 5.12.1
3. Initiated pre-view generation (occ preview:generate-all --path="/myuser/files/TestDir")
4. Checked nextcloud.log

Expected behaviour

Thumbnails to be generated

Actual behaviour

Nextcloud logs error, stating "Nextcloud allows only integer log levels". See attached file for detailed error entry.

error.json

Temporary workaround for the issue:
perl -i.bak -pe 's/$this->logger->log($this->logLevel,/$this->logger->log(4,/g'
./app/custom_apps/previewgenerator/lib/Support/OutputInterfaceLoggerAdapter.php