```
ezpublish/EzPublishKernel.php
It is not possible to just copy your old EzPublishKernel.php file over from the previous installation, since quite a few changes were made to this file in this release. We suggest that you simply reflect in the new kernel file any changes you made in the previous version.
```

ref: https://confluence.ez.no/display/EZP/Upgrading+from+5.1+to+5.2 (will hopefully be copied to EZP52 soon by Ricardo).